quarta-feira, 30 de janeiro de 2013

...o que pode ser informação?

Ainda não sei a resposta!


Eu estava querendo entender de uma vez por todas o que é informação para a CI. É uma coisa? Qualquer coisa? Um processo? Composto por quais etapas?
Bom, não consegui chegar a um consenso para minha "tosxonomia" da informação, permaneço com um punhado de conceitos perdidos e até contraditórios.

Dado, estímulo, mensagem, percepção, sentido, informação, interpretação, conhecimento. Não estão em ordem hierárquica e sei que alguns itens podem ter nada a ver com CI, ou podem ser subitens dos itens citados...

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Vamos começar pelo começo de tudo, pela teoria matemática da comunicação de Claude Shannon. Creia que ela tenha sido uma das primeiras a dar um sentido à "informação" diferente do senso comum.

É inegável a importância das teorias de Shannon para a tecnologia de compressão de dados – de onde podemos citar o mp3 e comunicação por telefonia celular.

O texto fui publicado em 1948, ou seja, pouco depois do artigo do Bush...

The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point. Frequently the messages have meaning; that is they refer to or are correlated according to some system with certain physical or conceptual entities. These semantic aspects of communication are irrelevant to the engineering problem. The significant aspect is that the actual message is one selected from a set of possible messages. The system must be designed to operate for each possible selection, not just the one which will actually be chosen since this is unknown at the time of design.

If the number of messages in the set is finite then this number or any monotonic function of this number can be regarded as a measure of the information produced when one message is chosen from the set, all choices being equally likely.

...ou seja, a preocupação é que a mensagem, enquanto dados ou sinais, chegue ao destinatário da mesma forma em que foi criada... o significado da mensagem, e, portanto, sua relação cognitiva com o receptor, não importa para essa teoria... Nela, informação e mensagem são conceitos distintos...



1. fonte de informação (information source) "An information source which produces a message or sequence of messages to be communicated to the receiving terminal. The message may be of various types: (a) A sequence of letters as in a telegraph of teletype system; (b) A single function of time f(t) as in radio or telephony;"


2. Transmissor (transmitter) – transmuta a mensagem para um sinal que opere no determinado canal – no telefone, a pressão sonora vira corrente elétrica.

3. Canal (channel) é o meio usado para transmitir o sinal do transmissor para o receptor – no caso da telefonia, são os fios

4. O receptor, faz a operação inversa do transmissor – reconstitui a mensagem a partir do sinal

5. Destinatário (destination) é a pessoa ou coisa para quem a mensagem foi pretendida
"reasonable measure of choice or information."



Kahlid Sayood explica a teoria de Shannon com um exemplo interessante:

"The barking of a dog during a burglary is a high-probability event and, therefore, does not contain too much information. However, if the dog did not bark during a burglary, this is a low-probability event and contains a lot of information."
SAYOOD, Khalid. Introdution to Data Compression. Morgan Kauffman. 2005.


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Fui procurar informação no As We May Think do Bush...

The real heart of the matter of selection, however, goes deeper than a lag in the adoption of mechanisms by libraries, or a lack of development of devices for their use. Our ineptitude in getting at the record is largely caused by the artificiality of systems of indexing. When data of any sort are placed in storage, they are filed alphabetically or numerically, and information is found (when it is) by tracing it down from subclass to subclass. It can be in only one place, unless duplicates are used; one has to have rules as to which path will locate it, and the rules are cumbersome. Having found one item, moreover, one has to emerge from the system and re-enter on a new path.

We know that when the eye sees, all the consequent information is transmitted to the brain by means of electrical vibrations in the channel of the optic nerve.

... aparentemente informação é uma coisa a ser encontrada a partir de dados sobre ela (claro, no contexto da biblioteca que ele usa como exemplo); lida com percepção visual da informação...



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Tenho todos os pés atrás com esses caras de Administração do Conhecimento, Mapeamento do Conhecimento e variáveis, mas o Karl-Erik Sveiby me poupou um trabalhão ao disponibilizar em seu website uma disputa entre os conceitos de informação de Weiner e Shannon (ambos do final de 1940):


Shannon defines information as a purely quantitative measure of communicative exchanges.

For an information theorist based on Shannon it does not matter whether we are communicating a fact, a judgement or just nonsense. Everything we transmit over a telephone line is "information". The message "I feel fine" is information, but "ff eeI efni" is an equal amount of information.

Shannon is said to have been unhappy with the word "information" in his theory. He was advised to use the word "entropy" instead, but entropy was a concept too difficult to communicate so he remained with the word. Since his theory concerns only transmission of signals, Langefors (1968) suggested that a better term for Shannon's information theory would therefore perhaps be "signal transmission theory.

But Shannon`s "information" is not even a signal (p.100):
If one is confronted with a very elementary situation where he has to choose on of two alternative messages, then it is arbitrarily said that the information, associated with this situation, is unity. Note that it is misleading (although often convenient) to say that one or the other message conveys unit information. The concept of information applies not to the individual messages (as the concept of meaning would), but rather to the situation as a whole, the unit information indicating that in this situation one has a freedom of choice, in selecting a message, which it is convenient to regard as a standard or unit amount.
Contradição entre Weaver e Shannon
Weaver, explaining Shannon`s theory in the same book:
Information is a measure of one's freedom of choice in selecting a message. The greater this freedom of choice, the greater the information, the greater is the uncertainty that the message actually selected is some particular one. Greater freedom of choice, greater uncertainty greater information go hand in hand.
There is thus one large - and confusing - difference between Shannon and Wiener. Whereas Wiener sees information as negative entropy, i.e. a "structured piece of the world", Shannon`s information is the same as (positive) entropy. This makes Shannon`s "information" the opposite of Wiener`s "information".How can something be interpreted as both positive entropy and negative entropy at the same time? The confusion is unfortunately fuelled by other authors.


As I interpret the cybernetic view, the signals in a system thus contain "information" - which have some meaning for the purpose of the particular system. Someone or a system outside the system may define a goal, but the meaning of the information that is sent/received within the system does not necessarily have a meaning outside the system. The information in the feedback loop has a meaning only in relation to the purpose. The goal of the subsystem is determined by a system on a higher level. The brain itself can be seen as such a suprasystem as long as it performs functions of temperature regulator etc.The signals controlling the muscle thus have no meaning outside the system of the muscle although the goal of the muscle is determined by a suprasystem like the brain. The only thing that the suprasystem "cares about" is whether the muscle fulfils its purpose or not.


"Meaning" in the cybernetic concept relates to a system of systems only. If the human being interferes with a purpose outside the system - it imposes an interpreted level of meaning outside the system. Wiener`s "information" presumes an observer with a meaning of his/her own outside the system who determines the goal of the system. The observer may be another machine but in the end (or perhaps beginning) there must be a human being somewhere with an intention or purpose. The observer`s meaning is thus interrelated with the system`s meaning. The signals of the system therefore have a relation to a human meaning, even if it can be very distant.


One of the conclusions from Shannon`s theory is that entropy contains more information than structure. It is a strange idea that goes against common sense. Let us first try to understand Shannon`s concept by seeing it in connection with human/human communication.Shannon presumes something/someone outside the transmission chain with a message which corresponds to "information". However, it is not information that is transmitted, but signals. There is a sender and a receiver of these signals. The sender`s meaning must be interpreted by the receiver outside the transmission itself. For doing this, both sender and receiver must have something in common - at least a language, otherwise they will not understand each other. If someone receives a meaningless expression via the telephone line there thus exists a very large number of possible interpretations. The information exists as a potential3 which of course is very large in a meaningless expression. If the expression on the other hand is crystal clear and the sender and the receiver share exactly the same understanding then there is very little information transmitted, only the signals themselves.The signals thus exist on another level than the information and the two have nothing to do with each other unless the code of meaning is shared from the beginning.Let us assume a natural system or object like a stone. The stone is meaningless in itself. Even a stone can thus be seen as "containing" an infinite number of potential meanings. It is a very large amount of "information" in Shannon`s sense. The stone may be measured, weighed observed etc. by humans down to the atomic level. The number of interpretations from such observations is equally infinite.

We will also see that the "sender" of the signals is not the stone but the human being`s apparatus. It would be an inconceivable task to transmit over a telephone line the entire possible amounts of data which make up the movements of the atoms which in their turn make up the object we call "stone". The object-called-stone exists as a source of potential information, which is not there until some human being interprets it, i.e. gives it meaning

All meaning is interpreted outside the transmission of signals. "Information" according to Shannon, must therefore not be confused with meaning. Shannon`s information relates not so much to what you do say as to what you could say (or do not say). The problems of interpreting signals into a "message" are left outside Shannon`s definition. Not so with Wiener. He assumes some meaning at least for the system level.

In order to get around the problem of meaning a common method is to contrast the word information with the word data. See for instance Schoderbek & al (1975/85, p.152). Data is according to them seen as:
unstructured, uninformed facts so copiously given out by the computer. Data can be generated indefinitely; they can be stored, retrieved, updated and again filed. They are a marketable commodity . . . each year the cost for data acquisition grows on the erroneous assumption that data are information.
The usage of the word information is by these authors restricted to facts with meaning or evaluated data. Information is connected to the circumstances of the receiver or user, whereas data exist independent of user. Data are seen as unevaluated pieces or materials, whereas information refers to data evaluated for a particular problem.

This distinction is problematic also because meaningful information for one user in a specific situation might be devoid of meaning for another user in another situation. What can be defined as information in one context becomes data in another. The same set of symbols might therefore be toggling between "data" and "information" depending on the circumstances.


A definition of this kind does not bring any further understanding. Other successors of Shannon have suggested mathematical theories which add "meaning" to his theory. One idea suggested by Brillouin 1956 (referred in Jumarie 1990) is to regard the amount of information as a function of the ratio of the number of possible answers before and after a communication has taken place. Information would then be the difference between the two.It might be this that Gregory Bateson referred4 to when he made his famous statement:
Brillouin also came up with a paradox: Suppose that a lenghty piece of information is sent as a text. The last item of the text is a bit which tells the receiver that all the text before the bit is untrue. Has any information been transferred then? Brillouin suggests an addition to Shannon`s theory which would take care of this: "negative" information.
Another concept along the same line is "relative" information introduced by Jumarie (1990). He tries to define a mathematical theory which incorporates "subjective transinformation" or a meaning that is relative to the receiver.
Information is a difference that makes a difference.

Barabba & Zaltman (1990) who are discussing the use of market research information and how one is to know whether the information gathered are "facts" or not. They propose a hierarchy that I have come across elsewhere: Data (numbers, words) lowest in the hierarchy, Information (statements), Intelligence (rules), Knowledge (combination of the levels below) and Wisdom (combined knowledge bases) highest in the hierarchy.

....Agora surge um exemplo interessante...


Let us assume the communication between a journalist, (= the sender of information), and a receiver (= reader/viewer of information).The world from a journalist`s point of view can be regarded as a chaos of physical objects, people, empirical data, facts, other people`s knowledge, theories, etc. The writer focuses on the particular piece of the world and uses his/her tacit knowing as a tool, when writing a text. The text in the article is the writer`s attempt to give meaning to a piece of the chaos.It is important to realise that the words of the text do not "contain" the tacit knowing of the writer, only the inaccurate articulation of it. The text becomes a blend of clues from the senses, the data and the concepts, rules and values of the journalistic profession. The blend is new tacit knowing created in the mind of the writer. The writer then tries to articulate this tacit knowing into a text. The structured text in the article will contain less knowledge than the writer knows and less information than the writer acquired.The reader will therefore read the words, but since he/she can not read the writer`s mind, the reader`s tacit knowledge will blend with the writer`s articulated knowledge and form "new" tacit knowing. The reader`s new process-of-knowing can never be the same as the writer`s but it might be similar. How close their knowing is depends on whether they share the same tradition, culture, knowledge, profession, business etc. This difference in semantic meaning has nothing to do with the technical communication, the noise level etc. - the difference occurs because of the inherent fuzziness of our language. (Fuzzy does not mean uncertain but different possible definitions of the same concept or categorisation, Vamos 1991).


...parece um pouco até com a teoria do Shannon, pois o jornalista codifica sua visão da "realidade" (que está na sua mente) e o leitor a descodifica (para sua mente). O problema é que a passagem mente-"papel" tem perdas por conta da língua, da habilidade do autor em expor etc; a descodificação feita pelo leitor também sofre, pois ele tem que dominar a lingua/linguagem, tem algum entendimento sobre o assunto em questão e captar o que o autor quis dizer... mensagem foi codificada (escrita), transmitida por um canal (jornal), recebida e descodificada.


The reader must reconstruct the meaning in a tacit process. The writer and the reader are not in direct contact however, and therefore much of the meaning gets lost. The text in an article or book is an attempt to communicate knowledge but the value lies not in the text or program itself but in what is not there, in the work the writer did when he/she tried to "make sense" of the chaos. The reader`s reconstruction is energy consuming and takes time. Therefore the reader must make a choice whether to read the text or not. The reader does not know before-hand whether it is worth spending time on. The choice will therefore have to based on something else than the text itself like: rumour, the name of the author, the medium, the context (at home, on vacation, in office etc.). (This is incidentally a feature also shared by services).


...sobre o excesso de "oferta de informação" que afeta o mundo hoje...


The situation in society today thus more resembles Shannon`s notion of information than Wiener`s.It is possible to make the analogy with the stone again. The massmedia "contain" an infinite amount of potential information, but the information is not communicated between a sender and a receiver in a relationship of mutual understanding. It is broadcasted from a sender and there it stops.The receiver is more like the observer of the stone I mentioned above. There are an infinite number of senders and channels and an infinite number of possible ways to measure and combine the signals. The signals have to be found, meaning must be interpreted by the receiver.

Although Information theory`s concepts cover only the technical level of communication they were developed for human/human communication. Especially cybernetic theory claims its closeness to the human brain.There are however several problems connected with the notion of information when it is used in a theory for human to human communication. Human/human communication is a question of interpretation and context:First, humans do not communicate with electric signals. Most of human to human communication in daily life is tacit (Polanyi 1967).Second, "signals" between people are manifold. They can be anything from speech to silence, from a hand wave to an unconscious twitch in the eye or a stern expressionless face.Third, the same signal may be interpreted differently by different individuals. Fourth, human communication involves a very complex interpretation by the "receiver". One school of thought, constructivism (see von Glaserfeld 1988), even regards communication as a construction in the mind of the individual.Fifth, people often "enact" their environment (Weick 1979). They impose their own ideas on others and then receive back clues that they have been constructing themselves. Communication may thus even be seen as going in the opposite direction, from receiver to sender.There are at least three arguments that speak in favour of Shannon`s original notion of information as having no connection with meaning at all.The meaning of a text or a table does not exist independently of the receiver as a fixed state. "Meaning" must somehow be constructed by the receiver. Every meaning is therefore unique for the human being interpreting it. The meaning can not be forecasted by someone else. This is implied in Shannon`s mathematical definition of information as a probability.


...então "sentido" é uma probabilidade?


There seems to be confusion among successors to Shannon as regards the mathematical consequences of his theory. If I interpret his theory according to his own texts, information is equal to entropy, i.e. chaos. Chaos contains no meaning.My own experience from the financial information markets is that they - from a receiver`s point of view - are more comparable to chaos than to structure.Information in the cybernetic sense then becomes a special case restricted to laboratory experiments with fixed settings and restricted boundaries or in manmade systems on the system`s level.

Information has No Value and No MeaningI have pointed at some arguments which speak in favour of regarding information as a potentiality, i.e. the way Shannon does. The implication from this is that there is more information in chaos and complexity than in structure, although this notion seems to go against a lot of the senses we call common. My own experience from the financial massmedia is however that the more information we produce, the more chaotic the world turns.The conclusion from following Shannon is that information has no value in itself. The value of information comes out mainly in connection with human action or as an indirect relation.A lot of what scientists have been working with in experimental psychology and the information sciences is based on the notion that information has a meaning or value independent of the user. If one follows Shannon`s notion, they have been studying special cases like the closed system or the level of reduced information only.A still unsolved issue is why (at least some) systems theorists seem to base their analysis on an interpretation of Shannon that goes against his theory.



Fonte

Karl-Erik Sveiby Oct 1994, updated 31 Dec 1998. All rights reserved.

Conceitos de informação para diversos autores:


O cara que fez esse mega apanhado – aqui resumido às definições que EU selecionei – é o Chaim Zins, que trabalha com "Knowledge Mapping"...


Albrechtsen (Dinamarca)
Information is related to meaning or human intention. In computational systems information is the contents of databases, the web etc. In human discourse systems information is the meaning of statements as they are intended by the speaker/writer and understood/misunderstood by the listener/reader.
Araújo (citada por FREIRES, p70)

 “[...] um processo constantemente reconstruído pelo sujeito do conhecimento, a partir de uma determinada realidade social e  de significativos pessoais. Informar-se, portanto, não é um processo finalizado quando o
sujeito do conhecimento recebe/usa a informação. Tal processo é algo aberto/inacabado  e,  como  tal,  sempre  propício  a  reestruturações;  caso  contrário  não  poderíamos  criar novas informações, uma vez que, as informações já existentes representariam a realidade  de forma completa e satisfatória” (ARAÚJO, 2002, p. 19).
http://rabci.org/rabci/sites/default/files/TCC-Freires.pdf 



Barber (Argentina)
Information is (1) a message used by a sender to represent one or more concepts within a communication process, intended to increase knowledge in recipients. (2) A message recorded in the text of a document...

...mensagem num processo comunicacional, e informação como coisa (Buckland) e até Informação = conhecimento registrado (Farradane)...


Barreto (Brasil)
(Eu mesmo coletei a definição)
Nesse sentido, tem-se procurado caracterizar a essência do fenômeno da informação como a adequação de um processo de comunicação que se efetiva entre o emissor e o receptor da mensagem. Assim, os diversos conceitos encontrados para a informação tendem a se localizar no começo e no fim do processo de comunicação (Wersing e Neveling, 1975).Aqui a informação é qualificada como um instrumento modificador da consciência do homem e de seu grupo. Deixa de ser uma medida de organização para ser a organização em si; é o conhecimento, que só se realiza se a informação é percebida e aceita como tal e coloca o indivíduo em um estágio melhor de convivência consigo mesmo e dentro do mundo em que sua historia individual se desenrola.Em uma relação temporal, a informação como partícula, que forma estoques, associa-se ao tempo linear, calendário; ao tempo dos fatos ocorridos cronologicamente. A informação acumula-se em estoques, de formação contínua, e agrega-se em uma estrutura ou repositório fixo. O volume e o crescimento destes estoques são diretamente proporcionais a um tempo contínuo, linear. Contudo, estes estoques emitem ondas de informação para atingir o homem e cumprir a sua missão de transformar partículas de informação em ondas de conhecimento. O tempo em que se opera a reflexão consciente para a assimilação de informação não é o tempo linear dos estoques de informação. O homem que reflete, como ser consciente, está colocado entre o passado e o futuro, em um tempo que se repete, quotidianamente cíclico, em um ponto imaginário de uma linha que une passado e futuro.
...o autor trata informação tanto como coisa como processo – todos os trechos são do "A questão da informação" de 1994.

Belkin (Citado por FREIRES p71)


“informação é uma mensagem propositadamente estruturada por um gerador e resultante da decisão  deste de  comunicar determinado  aspecto de seu estado de conhecimento, isolando-o e  modificando-o conforme sua intenção. Essa estrutura comunicável vai compor o corpo  de  conhecimentos  a  que receptores  em  potencial têm  acesso,  e  que  ao reconhecerem  uma  anomalia  em  seu  estado  de  conhecimento,  convertem-na  numa  estrutura comunicável (a pergunta), usando-a para recuperar do corpo de conhecimentos o que é apropriado para solucionar a anomalia, decidindo se está suficientemente resolvida - incerteza reduzida ou eliminada” (BELKIN, Nicholas J. citado por TARGINO, 2000, p. 7).

http://rabci.org/rabci/sites/default/files/TCC-Freires.pdf

Biagetti (ITÁLIA)
Datum is every thing or every unit that could increase the human knowledge or could allow to enlarge our field of scientific, theoretical or practical knowledge, and that can be recorded, on whichever support , or orally handed. Data can arouse information and knowledge in our mind.
Information is the change determined in the cognitive heritage of an individual. Information always develops inside of a cognitive system, or a knowing subject. Signs that constitute the words by which a document or a book has made are not information. Information starts when signs are in connection with an interpreter (Morris, 1938).
Knowledge Is structured and organized information that has developed inside of a cognitive system or is part of the cognitive heritage of an individual (based on C. S. Peirce, 1931, 1958).

...dado parece mensagem; informação começa quando sinais estão em conexão com um interpretador...

Bogdan (citado por CAPURRO e HJORLAND re-citado por FREIRES)


“a  noção  de  informação  tem  sido  usada  para  caracterizar  uma  medida  de  organização  física  (ou  sua  diminuição,  na  entropia), um padrão de comunicação entre fonte e receptor, uma forma de controle e  feedback,  a  probabilidade  de  uma  mensagem  ser  transmitida  por  um  canal  de  comunicação, o conteúdo de um estado cognitivo, o significado de uma forma lingüística  ou  a  redução  de  uma  incerteza”  (BOGDAN,  Radu  J.  citado  por  CAPURRO  e  HJORLAND, 2007, p. 160).

http://rabci.org/rabci/sites/default/files/TCC-Freires.pdf


Brookes (Citado por FREIRES)


a  informação  como  um  artefato  de  produção de efeitos, cuja influência incide na passagem de um estado de conhecimento para outro estado de conhecimento.

http://rabci.org/rabci/sites/default/files/TCC-Freires.pdf


Buckland (EUA)
Information. The word “information” is used to refer to a number of different phenomena. These phenomena have been classified into three groupings: (1) Anything perceived as potentially signifying something (e.g. printed books); (2) The process of informing; and (3) That which is learned from some evidence or communication. All three are valid uses (in English) of the term “information”. I personally am most comfortable with no. 1, then with no. 3, but acknowledge that others have used and may use no 2.


Burrell (Reino Unido)
Data are the basic individual items of numeric or other information, garnered through observation; but in themselves, without context, they are devoid of information. Information is that which is conveyed, and possibly amenable to analysis and interpretation, through data and the context in which the data are assembled. Knowledge is the general understanding and awareness garnered from accumulated information, tempered by experience, enabling new contexts to be envisaged.


Capurro (Alemanha)
Information is a multi-layered concept with Latin roots (`informatio' = to give a form) that go back to Greek ontology and epistemology (Plato's concept of `idea' and Aristotle's concepts of `morphe' but also to such concepts as `typos' and `prolepsis') (See Capurro, 1978; Capurro & Hjoerland, 2003). The use of this concept in information science is at the first sight highly controversial but it basically refers to the everyday meaning (since Modernity): “the act of communicating knowledge” (OED). I would suggest to use this definition as far as it points to the phenomenon of message that I consider the basic one in information science.

Message, information, understanding. Following systems theory and second-order cybernetics, I suggest to distinguish between `message', `information' and `understanding.' All three concepts constitute the concept of communication (See, for instance, Luhmann, 1996, with references to biology (Maturana/Varela), cybernetics etc.). A `message' is a `meaning offer' while `information' refers to the selection within a system and `understanding' to the possibility that the receiver integrates the selection within his/her pre-knowledge - constantly open to revision i.e. to new communication - in accordance with the intention(s) of the sender. The receiver mutates each time into a sender.


Data, information, knowledge. Putting the three concepts ("data", "information", and "knowledge") as done here, gives the impression of a logical hierarchy: information is set together out of data and knowledge comes out from putting together information. This is a fairytale.


Childers (EUA)
Knowledge is that which is known, and it exists in the mind of the knower in electrical pulses. Alternatively, it can be disembodied into symbolic representations of that knowledge (at this point becoming a particular kind of information, not knowledge). Strictly speaking, represented knowledge is informationKnowledgethat which is known—is by definition subjective, even when aggregated to the level of social, or public, knowledge—which is the sum, in a sense, of individual “knowings.”  Data and information can be studied as perceived by and “embodied” (known) by the person or as found in the world outside the person. 

...assim como Jason Farradane, informação seria conhecimento representado. Trata informação como coisa...


Davis (EUA)
Data is the plural of datum, although the singular form is rarely used. Purists who remember their first-year Latin may insist on using a plural verb with data, but they forget that English grammar permits collective nouns. Depending on the context, data can be used in the plural or as a singular word meaning a set or collection of facts. Etymologically, data, as noted, is the plural of datum, a noun formed from the past participle of the Latin verb dare—to give. Originally, data were things that were given (accepted as “true”). A data element, d, is the smallest thing which can be recognized as a discrete element of that class of things named by a specific attribute, for a given unit of measure with a given precision of measurement (Rush & Davis, [in progress]; Landry & Rush, 1970; Yovits & Ernst, 1970).”

Information The verb ‘inform’ normally is used in the sense to communicate (i.e., to report, relate, or tell) and comes from the Latin verb informare, which meant to shape (form) an idea. Data is persistent while information is transient, depending on context and the interpretation of the recipient. Information is data received through a communication process that proves of value in making decisions.

...informação é algo transitório, efêmero – pode ser um processo... para Shannon, a informação é uma probabilidade e aí trago o ótimo exemplo do Sayood: "The barking of a dog during a burglary is a high-probability event and, therefore, does not contain too much information. However, if the dog did not bark during a burglary, this is a low-probability event and contains a lot of information."


Dodig-Crnkovic (SUÉCIA)

Raw data (sometimes called source data or atomic data) is data that has not been processed for use. [In the spirit of Tom Stonier’s definition - Data: a series of disconnected facts and observations] Here “unprocessed” might be understood in a sense that no specific effort has been made to interpret or understand the data. They are the result of some observation or measurement process, which has been recorded as “facts of the world”. The word data is the plural of Latin datum, “something given”, which one also could call “atomic facts.Information is the end product of data processing.

... muito processamento de dados para o meu gosto...


Ess (EUA)
Prolog. These definitions are offered as an elaboration on physicist Heinz Pagels’ (1988) observation.
Information is just signs and numbers, while knowledge has semantic value. What we want is knowledge, but what we often get is information. It is a sign of the times that many people cannot tell the difference between information and knowledge, not to mention wisdom, which even knowledge tends to drive out. (1988, 49, cited in O’Leary and Brasher, 1996, 262).
Data can be defined as a class of information objects, made up of units of binary code that are intended to be stored, processed, and transmitted by digital computers. As such, data consists of information in a narrow sense – i.e., as inscribed in binary code, units of data are not likely to be immediately meaningful to a human being. But units of data, as “informational building blocks,” when collected and processed properly, can form information in the broader sense (see below), i.e., that is more likely to be meaningful to a human being (as sense-making beings).
  Information. Collocations of data (information in the narrow sense – see above) that thereby become meaningful to human beings – e.g., as otherwise opaque units of binary code are collected and processed into numbers, artificial and natural languages, graphic objects that convey significance and meaning, etc. Such collocations of data can be made meaningful by human beings (as sense-making beings) especially as such data collocations/information connect with, illuminate, and are illuminated by still larger cognitive frameworks – most broadly, worldviews that further incorporate knowledge and wisdom (see below). On this definition, information can include but is not restricted to data. On the contrary, especially as Borgmann (1999) argues, there are other forms of information (natural, cultural) that are not fully reducible to data as can be transmitted, processed, and/or produced by computers and affiliated technologies.
Knowledge is one step above information, and one step below wisdom. Knowledge in the broadest sense approaches a reasonably comprehensive worldview, i.e., a cognitive framework that establishes the major parameters and ten thousand details of human social and ethical realities, including basic values, beliefs, habits, notions of identity, relationships among human beings (including gender identity and issues) and relationships between humanity and larger realities (political, environmental, religious). Knowledge, however, can remain detached, objective, and thereby useless. Transforming cognitive forms of knowledge into ethical judgment and action is a primary task and goal of wisdom (see Dreyfus 2001; Ess 2003, 2004).” [16] (Charles Ess)
...eu fico na dúvida: qual a diferença entre Dado e estímulo?.. e o Capurro diz que a hierarquia informação -> conhecimento é conto de fadas...


Fidel (EUA)
Data are a string of symbols.
Information is data that is communicated, has meaning, has an effect, has a goal.           Knowledge is a personal/cognitive framework that makes it possible for humans to use information.




Harmon (EUA) (esse cara é de uma Ischool do Texas)
Data is one or more kinds of energy waves or particles (light, heat, sound, force, electromagnetic) selected by a conscious organism or intelligent agent on the basis of a pre-existing frame or inferential mechanism in the organism or agent.Information is an organism’s or an agent’s active or latent inferential frame that guides the selection of data for its own further development or construction.Knowledge is one or more sets of relatively stable information.
A Message is one or more inferred data sets gleaned from external or internal energetic reactions.


... eu diria que dado seria estímulo eficiente (para trabalharmos dentro da psicologia de Gibson) se não fosse pelo "pre-existing frame or inferential mechanism" que talvez ultrapassem a simples percepção (excitação por conta de estímulo). Mas também pode ocorrer que para certos estímulos serem efetivos, seja necessário inferir (generalizar, criar leis)...


Haythornthwaite (EUA)
Information. I would usually expect information to be an assessment or interpretation of data. Often information is not far removed from the ‘smallest collectable unit’ as I have defined “datum”. But I expect it to be some abstraction from data... Information does not inherently mean empirical or first hand analysis of data. It also does not guarantee correct interpretation of data although that is expected.A message is the encoded information or codified/explicit knowledge that is disseminated to others. Very much a Shannon and Weaver transmission model, but I also consider that encoding and decoding have a heavy personal, contextual and historical influence.

...ele trabalha a mensagem como sinal, código que representa informação ou conhecimento explícito... daí mensagem seria o aspecto linguístico da comunicação, enquanto informação seria a interpretação do significado...



Hersh (EUA)
Data are the raw observations about the world collected by scientists and others, with a minimum of contextual interpretation.
Information is the aggregation of data to make coherent observations about the world.Knowledge is the rules and organizing principles gleaned from data to aggregate it into information.

...não entendi...


Hjorland (Dinamarca)
Information. The most fruitful theoretical view is here based on Karpatschof's interpretation of information and activity theory, AT (2000, p. 128ff.). In order to define information, Karpatschof introduces the concept of release mechanisms, being systems having at their disposal a store of potential energy, the systems being ”designed” to let this energy out in specific ways, whenever trigged by a signal fulfilling the specifications of the release mechanism. The signal that triggers a certain release mechanism is a low energy phenomenon fulfilling some release specifications. The signal is thus the indirect cause, and the process of the release mechanism the direct cause of the resulting reaction, which is a high-energy reaction compared to the energy in the signal. Information is thus defined as a quality by a given signal relative to a certain mechanism.
The release mechanism has a double function: (1) it reinforces the weak signal and (2) it directs the reaction by defining the functional value of a signal in the pre-designed system of the release mechanism. There has been a tendency to consider information to be an obscure category in addition to the classical categories of physics. Information is indeed a new category, but it cannot be placed, eclectically, beside the prior physical categories. Information is a category, not beside, but indeed above the classical categories of physics. Therefore, information is neither directly reducible to these classical categories, nor is it a radically different category of another nature than mass and energy.
Information is, in fact, the causal result of existing physical components and processes. Moreover, it is an emergent result of such physical entities. This is revealed in the systemic definition of information. It is a relational concept that includes the source, the signal, the release mechanism and the reaction as its reactants. The release mechanism is a signal processing system and an information processing system.
Information is thus defined in physical terms of signals, mechanisms and energy, but probably first arose with the biological world. Hjørland (2002) outlines the development of information processing mechanisms in the biological, the cultural and the social world.
Many professionals can claim to work with "the generation, collection, organization, interpretation, storage, retrieval, dissemination, transformation and use of information". This is not specific to information professionals. (Their specific work is discussed in Capurro & Hjørland (2003) and elsewhere). Hjørland (2000) investigates when and why the word "information" became associated with library schools (and thus knowledge organization) and what the theoretical implications in the shift from documents to information imply”.

...informação seria um processo que envolve fontes, sinais, estímulos e resposta a eles (release mechanism and the reaction)...

Lara (citado por FREIRES)

“quando  reconhecida  como  inscrição  organizada,  a  informação  é  vista  como resultado  de  uma  ‘construção institucional  e intencional  que  tem nos valores simbólicos e funcionais a condição para a construção do sentido e para  circular socialmente, desencadeando processos de conhecimento’” (LARA, M. L. G. de  citada por LARA, 2007, p. 3).
Le Coadic (França)
Datum (in our sector mainly electronic) is the conventional representation, after coding (using ASCII, for example), of information.
Informação é  um  significado  transmitido  a  um ser  consciente  por meio  de  uma mensagem  inscrita  em um suporte  espacial-temporal: impresso, sinal elétrico, onda sonora, etc. Inscrição feita graças a um  sistema de signos (a linguagem), signo este que é um elemento da linguagem que associa  um significante a um significado” (LE COADIC, 2000, p. 4 citado por FREIRES).
Knowledge is the result of forming in mind an idea of something (Le Coadic, 2004).
...assim como Farradane, informação é conhecimento registrado num suporte; dado é a representação da informação (representação no sentido de descritores e recuperação?)...

Citação sobre informação: http://rabci.org/rabci/sites/default/files/TCC-Freires.pdf


Lorenz (República Tcheca)
Information is a relationship between an inner arrangement (i.e., a priori set structure (Smajs & Krob, 2003), implicate order of a system and its present embodiment in reality (explicate order) including mediating memory processes (i.e., historically dependent processes) releasing the meaning.

... parte do conceito de a priori, que pode ser encontrado em Kant (a priori é o contrário do empírico, é algo que se sabe sem ver, como conceito de espaço)... informação como processo, mas diria que ficou parecido com interpretação...


Marcondes (Brasil) 
(eu mesmo peguei a definição: Linguagem e Documento: fundamentos evolutivos e culturais da Ciência da Informação. Perspectivas em Ciência da Informação v.15, p 2-21, 2010 e do livro Documento: Gênese e Contextos de Uso vol. 1, 2010)
...informação, no contexto que possa interessar à Ciência da Informação, não é uma coisa, é um processo, o processo de interpretar fenômenos potencialmente informativos por um usuário.
Informação assim é um processo, não uma coisa, é o processo de informar(-se) através de coisas que são potencialmente informativas, em especial, de artefatos criados com a intenção precípua de informarem de modo mediado (através do tempo e do espaço), os documentos. 



Menou (França)
Information is recorded and organized data that can be communicated (Porat & Rubin, 1977). However, it is advisable to distinguish between the various states or conditions of information (e.g. information-as an object (Buckland, 1991b), or semantic, syntactic and paradigmatic states (Menou, 1995).Knowledge is information that is understood, further to its utilization, stored, retrievable and reusable under appropriate circumstances or conditions..

...começa numa acepção de processamento de dados (informação é dado trabalhado); passa pelos estados e condições da informação e diz que conhecimento é informação, entendida, armazenada e recuperável – mas não para saber se o autor fala de um processo humano ou se o conhecimento está numa biblioteca, por exemplo...


Moukdad (Canadá)
Information is facts, figures, and other forms of meaningful representations that when encountered by or presented to a human being are used to enhance his/her understanding of a subject or related topics.

...pode ser qualquer coisa que pode ser útil a alguém...


Oppenheim (Reino Unido)
Data are raw material of information, typically numeric.Information is data which is collected together with commentary, context and analysis so as to be meaningful to others.
Knowledge is a combination of information and a person's experience, intuition and expertise.
...aqui vê-se a informação como dado trabalhado e conhecimento como a combinação da informação com a parte cognitiva da pessoa... mas se humanos trabalham com dados para transformá-los em informação, isso não seria a "combination of information and a person's experience, instuition and expertise"?..

Oliveira (citada por FREIRES)


 “[...]  na  ótica  da  Ciência  da  Informação, o objeto ‘informação’ é uma representação. Como é uma representação do conhecimento, que  já  é uma representação do real, ela se torna uma representação de  representação” (OLIVEIRA, 2005, p. 18).

Disponível em http://rabci.org/rabci/sites/default/files/TCC-Freires.pdf


Pinheiro (Brasil)
Datum is an object or crude fact perceived by the subject, non – constructed nor elaborated in the consciousness, without passing through neither analysis processes nor evaluation for its transfer as information.Information is a phenomenon generated from knowledge and integrated therein, analyzed and interpreted to achieve the transfer process of message (i.e., meaningful content) and the cognitive transformations of people and communities, in a historical, cultural and social context.Knowledge is a social and cognitive process formed by the passing or assimilated information to thought and to action.Message is the meaningful content of information...

...temos dado quase como estímulo; informação como processo; mas não entendi direito parte de que a mensagem seria o conteúdo significativo da informação (penso ser o contrário)... queria saber de quais textos dela o Zins consultou...


Pinto (Espanha)
Data are primitive symbolic entities, whose meaning depend on it integration within a context that allow their understanding by an interpreter.Information is the intentional composition of data by a sender with the goal of modifying the knowledge state of an interpreter or receiver.Knowledge is the intelligent information processing by the receiver and it consequent incorporation to the individual or social memory (Belkin & Robertson, 1976; Blair, 2002).

...aqui dado é algo que depende do contexto para ser entendido pelo interpretador; informação é a intenção dada pelo "autor" com o objetivo de de modificar as estruturas de conhecimento do interpretador/receptor...


Poli (Itália)
Information. Def. 2. x is an item of information = x is a datum in adistal context. Definition 2 tells us that information is made up of more structured items. That is to say, information is the embedding of signs-in-a-proximal-context (i.e., data) in a distal context. Information, thus, adds greater structure to data. These definitions provide a first explanation for the scant interest aroused by proposals to draw more exact distinctions between data and information. In effect, in concrete cases of application, it is often difficult to distinguish precisely between distal and proximal contexts.
Conditions of knowledge. Knowledge is apparently not reducible solely to information and data. The problem is to understand 'what is lacking', what must be added to information and data in order to achieve true knowledge. My claim is that the meaning of a sign is given by the position of the sign in a field of signs (in a space). On the other hand, the content of a sign is given by the position of the item (denoted by the sign) in a field of items. Data, information, meanings and contents cover the field of knowledge. This amounts to saying that we have knowledge when we know (1) which item is denoted by which sign, (2) the item's proximal context, (3) the item's distal contexts, (4) the sign's position in the field of signs, (5) the item's position in the field of items (Poli, 2001).
Data, information, knowledge, message. I am unable to understand why data, information, knowledge and message are placed on the same level of analysis. I would suggest considering message as the “vehicle” carrying either data or information (which can be taken as synonymous). Knowledge hints to either a systematic framework (e.g., laws, rules or regularities, that is higher-order “abstractions” from data) or what somebody or some community knows (“I know that you are married”). In this latter sense knowledge presents a “subjective” side.
...entendi quase nada... aqui mensagem é veículo que carrega dados ou informação (sendo sinônimos)...


Rousseau (Bélgica)
Data are a representation of facts or ideas in a formalized manner, and hence capable of being communicated or manipulated by some process. So: data is related to facts and machines ( Holmes, 2001).Information is the meaning that a human assigns to data by means of the known conventions used in its representation. Information is related to meaning and humans (Holmes, 2001).

...aqui dado parece como mensagem; informação quase como interpretação...

Sfez (nas palavras de GOMES, 2010)


...a informação está situada entre o que poderia ser comunicado e o que é efetivamente expressado. Portanto, é o resultado da seleção que se faz entre as possibilidades de conteúdos a serem comunicados e a liberdade de escolha de cada palavra a ser dita, o que intervém na própria mensagem. A informação pode, frente à complexidade que surge no processo de significação, representar para o que Sfez chamou de “organismo auto-referente”, a reorganização dos significados já incorporados mentalmente.


Henriette Ferreira Gomes - http://www.dgz.org.br/jun10/Art_03.htm


Sturges, (UK)
Data are discrete items of information that I would call facts on some subject or other, not necessarily set within a fully worked out framework.Information is facts and ideas communicated (or made available for communication).Knowledge is the considered product of information. Selection as to what is valid and relevant is a necessary condition of the acquisition of knowledge.

...informação é o que é comunicado (quase como informação é o conteúdo do documento)...


Vieira (Brasil)
Data are representations of facts and raw material of information.Information is data organized to produce meaning.Knowledge is meaningful content assimilated for use. The three entities can be viewed as hierarchical in terms of complexity, data being the simplest and knowledge, the most complex of the three. Knowledge is the product of a synthesis in our mind that can be conveyed by information, as one of many forms of its externalization and socialization.

...trabalha com informação como dados organizados para produzir significado...


Wormell (SUÉCIA)
Data are alphabetic or numeric signs, which without context do not have any meaning.Information is a set of symbols that represent knowledge. Information is what context creates/gives to data. It is cognitive. Normally it is understood as a new and additional element in collecting data and information for planned action.Knowledge is enriched information by a person's or a system's own experience. It is cognitive based. Knowledge is not transferable, but through information we can communicate about it. (Note that the highest level of information processing is the generation of wisdom, where various kinds of knowledge are communicated and integrated behind an action.


...dados são sinais, caracteres, talvez mensagem... informação conjunto de símbolos que representam conhecimento – mas tem um plus: "information is what context creates/gives to data", ou seja, é subjetivo/cognitivo... ao mesmo tempo que se aproxima de Farradane (informação=conhecimento registrado), traz o caráter subjetivo da informação...


Wu (China)
Data are artifacts that reflect a phenomenon in natural or social world in the form of figures, facts, plots, etc.Information is anything communicated among living things.It is one of the three mainstays supporting the survival and evolution of life, along with energy and materials.Knowledge is a human construct, which categorize things, record significant events, and find causal relations among things and/or events, etc. in a systematic way.
...dados seriam estímulos ou mensagens?.. informação é qualquer coisa comunicada entre seres vivos... conhecimento é um constructo humano...


Fonte:
http://www.success.co.il/is/dik.html


Quadrinho baseado nas fontes que consultei




sexta-feira, 11 de janeiro de 2013

Compressão de dados


Desde os tempos do DOS e dos disquetes eu sempre tive curiosidade sobre como funciona a compressão de dados. Eu tentava imaginar mais ou menos como deveria ser o método de compactação, mas nunca tinha procurado, efetivamente, saber como se dá. Ao procurar um outro assunto, sem querer, encontrei um livro que me permitiu sair do âmbito da minha imaginação para acabar na de outrem - de um cara que realmente sabe como funciona o processo de compressão de dados.

Khalid Sayood - Introdution to Data Compression (2005)

O autor discorre sobre a transformação que os meios de comunicação têm sofrido e citando a Internet, a comunicação móvel e a comunicação por vídeo e afirma que a compressão de dados é uma das tecnologias que permitem essa revolução multimídia. Seria impossível colocar tanta informação como imagens, áudio e vídeo em websites sem algoritmos de compressão de dados. Até mesmo os celulares e a TV digital realizam compressão de dados.

Make a long-distance call and you are using compression. Use your modem, or your fax machine, and you will benefit from compression. Listen to music on your mp3 player or watch a DVD and you are being entertained courtesy of compression.

A compressão de dados está por todo lado. São os JPEGs e os MPEGs, os Zips e RARs. O que variam são as metodologias e algoritmos utilizados para reduzir o número de bits utilizados para representar uma imagem, vídeo ou música.

In brief, data compression is the art or science of representing information in a compact form. We create these compact representations by identifying and using structures that exist in the data. Data can be characters in a text file, numbers that are samples of speech or image waveforms, or sequences of numbers that are generated by other processes. The reason we need data compression is that more and more of the information that we generate and use is in digital form—in the form of numbers represented by bytes  of data. And the number of bytes required to represent multimedia data can be huge. For example, in order to digitally represent 1 second of video without compression (using the CCIR 601 format), we need more than 20 megabytes, or 160 megabits. If we consider the number of seconds in a movie, we can easily see why we would need compression. To represent 2 minutes of uncompressed CD-quality music (44,100 samples per second, 16 bits per sample) requires more than 84 million bits. Downloading music from a website at these rates would take a long time.

Sobre o corte de frequências "inaudíveis", como ocorre com o mp3, o autor

Many times, for example, when transmitting or storing speech and images, the data are intended to be perceived by a human, and humans have limited perceptual abilities. For example, we cannot hear the very high frequency sounds that dogs can hear. If something is represented in the data that cannot be perceived by the user, is there any point in preserving that information? The answer often is "no." Therefore, we can make use of the perceptual limitations of humans to obtain compression by discarding irrelevant information.
O autor assinala que as técnicas de compressão são formadas por dois algoritmos: um que gera a compressão, e outro que descomprime, conforme imagem abaixo:














A compressão de dados é divida em dois grandes grupos: Sem perda (Lossless) e Com perdas pequenas (Lossy). A "sem perdas" é utilizada, por exemplo, no caso da compactação de um texto, pois o original e o reconstruído não podem ter diferenças. Essa eficiência em reapresentar, porém, tem uma contrapartida: a razão de compactação é menor do que a alcançada pela "com perdas".
Lossless compression is generally used for applications that cannot tolerate any difference between the original and reconstructed data. Text compression is an important area for lossless compression. It is very important that the reconstruction is identical to the text original, as very small differences can result in statements with very different meanings. Consider the sentences "Do not send money" and "Do now send money." A similar argument holds for computer files and for certain types of data such as bank records.
Lossy compression techniques involve some loss of information, and data that have been compressed using lossy techniques generally cannot be recovered or reconstructed exactly. In return for accepting this distortion in the reconstruction, we can generally obtain much higher compression ratios than is possible with lossless compression. In many applications, this lack of exact reconstruction is not a problem. For example,
when storing or transmitting speech, the exact value of each sample of speech is not necessary. Depending on the quality required of the reconstructed speech, varying amounts of loss of information about the value of each sample can be tolerated. If the quality of the reconstructed speech is to be similar to that heard on the telephone, a significant loss of information can be tolerated. However, if the reconstructed speech needs to be of the quality heard on a compact disc, the amount of information loss that can be tolerated is much
lower. Similarly, when viewing a reconstruction of a video sequence, the fact that the reconstruction is different from the original is generally not important as long as the differences do not result in annoying artifacts. Thus, video is generally compressed using lossy compression.
O autor indica que o desenvolvimento de algoritmos para compressão é dividido em duas fases: modelagem (modeling) e codificação (coding). Na primeira, são procuradas e descritas as redundâncias no conjunto de dados. Na segunda fase, o modelo é descrito, ou seja, é mostrado como os dados são diferentes do modelo codificado. Seguem os exemplos:




















The sequence does not seem to follow a simple law as in the previous case. However, each value is close to the previous value. Suppose we send the first value, then in place of subsequent values we send the difference between it and the previous value. The sequence of transmitted values would be





Example 1 . S . S :
Suppose we have the following sequence:
abarayaranbarraybranbfarbfaarbfaaarbaway
which is typical of all sequences generated by a source. Notice that the sequence is made up of eight different symbols. In order to represent eight symbols, we need to use 3 bits per symbol. Suppose instead we used the code shown in Table 1.1. Notice that we have assigned a codeword with only a single bit to the symbol that occurs most often, and correspondingly longer codewords to symbols that occur less often. If we substitute the codes for each symbol, we will use 106 bits to encode the entire sequence. As there are 41 symbols in the sequence, this works out to approximately 2.58 bits per symbol. This means we have obtained a compression ratio of 1.16:1.















When dealing with text, along with statistical redundancy, we also see redundancy in the form of words that repeat often. We can take advantage of this form of redundancy by constructing a list of these words and then represent them by their position in the list. This type of compression scheme is called a dictionary compression scheme. 

Uma coisa interessante no livro é a explicação da Teoria da Informação de Shannon:

Although the idea of a quantitative measure of information has been around for a while, the person who pulled everything together into what is now called information theory was Claude Elwood Shannon [7], an electrical engineer at Bell Labs. Shannon defined a quantity called self-information. Suppose we have an event A, which is a set of outcomes of some random experiment. If P{A) is the probability that the event A will occur, then the self-information associated with A is given by

...let's see if the use of a logarithm in this context makes sense from an intuitive point of view. Recall that log(l) = 0, and — log(x) increases as x decreases from one to zero. Therefore, if the probability of an event is low, the amount of self-information associated with it is high; if the probability of an event is high, the information associated with it is low. Even if we ignore the mathematical definition of information and simply use the definition we use in everyday language, this makes some intuitive sense. The barking of a dog during a burglary is a high-probability event and, therefore, does not contain too much information. However, if the dog did not bark during a burglary, this is a low-probability event and contains a lot of information. (Obviously, Sherlock Holmes understood information theory!) Although this equivalence of the mathematical and semantic definitions of information holds true most of the time, it does not hold all of the time. For example, a totally random string of letters will contain more information (in the mathematical sense) than a well-thought-out treatise on information theory.
*grifo meu


Outra passagem que considerei interessante é a acerca da percepção humana, quando o autor explica como funcionam a visão e audição humanas. Ter conhecimento do funcionamento dos sentidos é importante, como indica o autor, para saber o que não é percebido - e assim saber o que pode ser cortado numa compressão "com perdas". Mas entender a percepção humana vai além do uso para compressão "com perdas". Em CI, é um conhecimento importante pois pode auxiliar na produção de documentos "mais visualizáveis"; na elaboração de interfaces de sistemas informatizados; e na criação de descrições e relatórios que substituam documentos. Pode também auxiliar estudos sobre eficácia, eficiência e relevância da informação (ver SARACEVIC, 2009), pois a percepção do usuário pode ser fator crítico no seu julgamento do que é ou não relevante - pois ele pode não perceber "de cara" o que é relevante para si.

The eye is a globe-shaped object with a lens in the front that focuses objects onto the retina in the back of the eye. The retina contains two kinds of receptors, called rods and cones. The rods are more sensitive to light than cones, and in low light most of our vision is due to the operation of rods. There are three kinds of cones, each of which are most sensitive at different wavelengths of the visible spectrum. The peak sensitivities of the cones are in the red, blue, and green regions of the visible spectrum [93]. The cones are mostly concentrated in a very small area of the retina called the fovea. Although the rods are more numerous than the cones, the cones provide better resolution because they are more closely packed in the fovea. The muscles of the eye move the eyeball, positioning the image of the object on







the fovea. This becomes a drawback in low light. One way to improve what you see in low light is to focus to one side of the object. This way the object is imaged on the rods, which are more sensitive to light. The eye is sensitive to light over an enormously large range of intensities; the upper end of the range is about 10^^ times the lower end of the range. However, at a given instant we cannot perceive the entire range of brightness. Instead, the eye adapts to an average brightness level. The range of brightness levels that the eye can perceive at any given instant is much smaller than the total range it is capable of perceiving. If we illuminate a screen with a certain intensity / and shine a spot on it with different intensity, the spot becomes visible when the difference in intensity is A/. This is called the just noticeable difference (jnd). The ratio y is known as the Weber fraction or Weber ratio. This ratio is known to be constant at about 0.02 over a wide range of intensities in the absence of background illumination. However, if the background illumination is changed, the range over which the Weber ratio remains constant becomes relatively small. The constant
range is centered around the intensity level to which the eye adapts. If Y is constant, then we can infer that the sensitivity of the eye to intensity is a logarithmic function {d{\ogI) = dl/I). Thus, we can model the eye as a receptor whose output goes to a logarithmic nonlinearity. We also know that the eye acts as a spatial lowpass filter [94, 95]. Putting all of this information together, we can develop a model for monochromatic vision, shown in Figure 8.2. How does this description of the human visual system relate to coding schemes? Notice that the mind does not perceive everything the eye sees. We can use this knowledge to design compression systems such that the distortion introduced by our lossy compression scheme is not noticeable.*grifo meu

Auditory Perception
The ear is divided into three parts, creatively named the outer ear, the middle ear, and the inner ear. The outer ear consists of the structure that directs the sound waves, or pressure waves, to the tympanic membrane, or eardrum. This membrane separates the outer ear from the middle ear. The middle ear is an air-filled cavity containing three small bones that provide coupling between the tympanic membrane and the oval window, which leads into the inner ear. The tympanic membrane and the bones convert the pressure waves in the air to acoustical vibrations. The inner ear contains, among other things, a snail-shaped passage called the cochlea that contains the transducers that convert the acoustical vibrations to nerve impulses.
The human ear can hear sounds from approximately 20 Hz to 20 kHz, a 1000:1 range of frequencies. The range decreases with age; older people are usually unable to hear the higher frequencies. As in vision, auditory perception has several nonlinear components. One is that loudness is a function not only of the sound level, but also of the frequency. Thus, for example, a pure 1 kHz tone presented at a 20 dB intensity level will have the same apparent loudness as a 50 Hz tone presented at a 50 dB intensity level. By plotting the amplitude of tones at different frequencies that sound equally loud, we get a series of curves called the Fletcher-Munson curves [96]. Another very interesting audio phenomenon is that of masking, where one sound blocks out or masks the perception of another sound. The fact that one sound can drown out another seems reasonable. What is not so intuitive about masking is that if we were to try to mask a pure tone with noise, only the noise in a small frequency range around the tone being masked contributes to the masking. This range of frequencies is called the critical band. For most frequencies, when the noise just masks the tone, the ratio of the power of the tone divided by the power of the noise in the critical band is a constant [97]. The width of the critical band varies with frequency. This fact has led to the modeling of auditory perception as a bank of band-pass filters. There are a number of other, more complicated masking phenomena that also lend support to this theory (see [97, 98] for more information). The limitations of auditory perception play a major role in the design of audio compression algorithms. 
O livro, obviamente não se limita apenas ao que coloquei - pelo contrário - o limitado aqui sou eu, pois não entendi nem os símbolos usados nas equações "tipo NASA" que permeiam toda a obra. Lá tem muita informação sobre inúmeros métodos, tipo e algoritmos de compressão de dados. Percorrem texto, som, vídeo, imagem... Não sou capaz de dizer que o livro é bom para os entendidos, mas para um leigo como eu, achei que os 10% que folheei foram mais do que suficientes para diminuir minha ignorância em relação ao assunto. 

SAYOOD, Khalid. Introdution to Data Compression. Morgan Kauffman. 2005.


Saracevic,.T. (2009). Information science. In: Marcia J. Bates and Mary Niles Maack (Eds.) Encyclopedia
of Library and Information Science. New York: Taylor & Francis. pp. 2570-2586. Disponível em: http://comminfo.rutgers.edu/~tefko/SaracevicInformationScienceELIS2009.pdf


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