4 C H A P T E R 1. P R O B A B I L I S T I C I N F O R M A T I C S 1.1 W h a t Is I n f o r m a t i c s ? In much of western Europe, informatics has come to mean the rough trans- lation of the English "computer science," which is the discipline that studies computable processes. Certainly, there is overlap between computer science programs and informatics programs, but they are not the same. Informatics programs ordinarily investigate subjects such as biology and medicine, whereas computer science programs do not. So the European definition does not suffice for the way the word is currently used in the United States. To gain insight into the meaning of informatics, let us consider the suffix "-ics," which means the science, art, or study of some entity. For example, "linguistics" is the study of the nature of language, "economics" is the study of the production and distribution of goods, and "photonics" is the study of electromagnetic energy whose basic unit is the photon. Given this, informatics should be the study of information. Indeed, WordNet 2.1 defines informat- ics as "the science concerned with gathering, manipulating, storing, retrieving and classifying recorded information." To proceed from this definition we need to define the word "information." Most dictionary definitions do not help as far as giving us anything concrete. That is, they define information either as knowledge or as a collection of data, which means we are left with the situation of determining the meaning of knowledge and data. To arrive at a concrete definition of informatics, let's define data, information, and knowledge first. By datum we mean a character string that can be recognized as a unit. For example, the nucleotide G in the nucleotide sequence GATC is a datum, the field "cancer" in a record in a medical data base is a datum, and the field "Gone with the Wind" in a movie data base is a datum. Note that a single character, a word, or a group of words can be a datum depending on the particular application. Data then are more than one datum. By information we mean the meaning given to data. For example, in a medical data base the data "Joe Smith" and "cancer" in the same record mean that Joe Smith has cancer. By knowledge we mean dicta which enable us to infer new information from existing information. For example, suppose we have the following item of knowledge (dictum): 1 IF t h e s t e m of the plant is woody A N D the position is upright A N D there is one m a i n t r u n k T H E N the plant is a tree. Suppose further that I am looking at a plant in my backyard and I observe that its stem is woody, its position is upright, and it has one main trunk. Then using the above knowledge item, we can deduce the new information that the plant in my backyard is a tree. Finally, we define informatics as the discipline that applies the method- ologies of science and engineering to information. It concerns organizing data 1Such an item of knowledge would be part of a rule-based expert system.