Information systems technology grounded on institutional facts - Information Systems Foundations: Constructing and Criticising - page 78

global scale we need to understand why the technology is so successful on a local scale,
and why it is difficult to adapt to an organisation-wide or larger scale.
Success at the local scale
Why are logical databases the technology of choice for implementing information sys-
tems?
Information systems are generally about the management of records. Records can be
records of just about anything: a company's accounts, medical records, criminal records,
a census, the archives of a newspaper, or the contents of a museum. Just about anything
can be a record; the Babylonians used clay tablets to record their business dealings, some
medical records are images, most of the contents of most museums are physical artefacts
of various kinds. But contemporary information systems are generally concerned with
documents that contain most of their information in the form of text. Physical objects
like the contents of a museum are generally represented in information systems by
documents called catalogue entries.
So, more specifically, information systems are about the management of records that are
documents containing information mostly in textual form. The general technology for
processing collections of text records is the text database.
The model of information-seeking behaviour supported by text databases has the follow-
ing steps:
1. The user has an information need.
2. The user formulates the information need as a query consisting of a collection of
terms.
3. The system returns the subset of its collection of documents containing all and only
those documents that contain the query terms.
4. The user then reviews the documents returned, and makes a judgment as to
whether each document satisfies the information need or not. The expectation is
that many of the documents returned will be irrelevant ( limited precision ). The ex-
pectation is also that some of the documents in the collection that would have sat-
isfied the information need were not returned, because the query did not contain
appropriate terms ( limited recall ).
Precision and recall are measured on a percentage scale. A precision of 0% means that
none of the documents retrieved met the information need. A precision of 100% means
that all did. A recall of 0% means that none of the relevant documents were retrieved.
A recall of 100% means that all were. Returning the entire collection guarantees 100%
recall, but gives a very low precision. Text database systems are considered to perform
very well if their average precision and average recall are as high as 40%.
Computer-based information systems generally make use of technologies such as rela-
tional databases. There is a wide variety of such systems, but they are generally charac-
terised by data models based on classes and instances, with relationships among classes.
Typically the data model is expressed in a language like UML, one of the varieties of
entity-relationship modeling, or object-role modeling. The populations of particular
systems are generally managed by systems based more or less on the first-order predicate
calculus, such as relational database systems or object-oriented database systems, which
we here call logical databases .
In text database terms, a query on a logical database is expected to have 100% precision
and 100% recall. A class list is the definitive statement of which students are enrolled