EXPRESS information bases
EXPRESS information bases
One of the assumptions underlying EXPRESS is that there is, somewhere, going to be an information base that contains instances of data corresponding to the information model. In this Chapter we examine aspects of this hypothetical information base. We also briefly note some of the software tools that could be useful when you are modeling using EXPRESS. We use the term information base in a very general sense; it is any repository that contains data corresponding to an EXPRESS (or EXPRESS-G) information model. The idea that probably comes to mind when hearing the term is that ‘an information base is a fancy name for a database.’ In our sense, an information base may be a database, but it may also be more than or less than a database. In fact, it may not even be computer-based at all! Some examples of information bases are: • Intelligent Knowledgebases • Knowledgebases • Databases • Computer files • Printed documents These examples are listed in approximately decreasing order of technical complexity and increasing order of technology age. Thus, intelligent knowledgebases are at, or even beyond, the leading edge of technology, while printed documents have been available for some centuries, although the technology for producing these has made dramatic strides over the last decade. Below we briefly describe various types of information bases, starting with databases. Knowledgebases are at the leading edge of the technology and are not treated; we merely note that there appears to be no fundamental reason why EXPRESS models should not be stored and instanced using this advanced technology. Databases provide a structured means of both storing data in a computer system and of querying the data in an efficient manner. Internally, the data may be structured in the form of a network, a hierarchy, or in tables following the relational model. Most new databases are relational, while older ones may be hierarchical or network based. Object-Oriented databases have recently appeared, but as yet there appears to be no consensus on exactly what an OODB is. Databases are designed so that they can be modified and queried by mutiple users.
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