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F IGURE 10.8
Data dictionary sample entities
In contrast, an
active data dictionary
is one that interacts with the IS
environment on a real-time basis. The nature of the interaction can involve input
into the data dictionary, output from it, or both. When a data dictionary is active
in terms of input, an event taking place in the IS environment, such as the creation
of a new database table, automatically results in new data (about this event)
being input into the data dictionary. When a data dictionary is active in terms of
output, responses from the dictionary are an integral part of the running of the IS
environment. For example, the data dictionary may contain data about who in the
company is authorized to access particular tables. If the data dictionary must be
''consulted'' for this data every time someone tries to access a table, then the data
dictionary is considered active in the output sense.
Entities and Attributes
In the earlier example, we discussed tables and attributes
as two possible data dictionary entities. Figure 10.8 shows a broader range of
possibilities. This is not intended to be a complete list that fits the needs of all
companies. In fact, one of the principles of the data dictionary concept is to make
the data dictionary expandable and customizable to a company's particular needs.
There are two classes of attributes for data dictionary entities: those that are
of a general nature and are likely to apply to any of the entities and those that are
specific to particular data dictionary entities. An example of a general attribute is
''Name.'' Most data dictionary entities must have a name or some other identifier.
By far most data dictionary attributes, however, are specific to particular entities.
Some examples include the Value Range of a numeric attribute, the Length of a
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