This index/glossary provides a simple definition of
many terms. It is linked from and to references throughout the OLAIS
materials. You can jump to any letter from the list below or jump
back to the top of the index from any letter heading in the listed
topics.
The zoom
icon
it links to documents where the defined term is used.
An entity used to represent an association or relationship between
other entities. Thus the associative entity has a relationship to each
of the other entities which are being associated. The associative relationships
are frequently (although not necessarily) modeled as dependent.
An associative entity can be modeled in place of a many-to-many
relationship. This has several important advantages. Unlike a relationship,
the associative entity can have attribut of its own (in addition to those
acquired indirectly by its relationships) and can also engage in relationships
other than those which form it.
Cardinal is one of several terms used for the quantification
of entity relationships. In general, where a relationship exists between
two entities, for each entity we must specify in some manner the minimum
and maximum number of occurrences in the entity which take part
in that relationship.
In some methodologies these quantities are called "connectivity";
in others, "cardinal" means the same thing. PowerDesigner
uses Cardinal specifically for the maximum occurences;
the minimum is referred to as the relationship's Existence.
For each supported DBMS product, PowerDesigner provides an external
plain text file with .DEF as the file extension (e.g., "SYBASE10.DEF").
This ".DEF" file contains numerous parameters and templates which
PowerDesigner employs to translate a CDM in to a PDM valid for the
target DBMS and to generate DDL/DML from the PDM.
Dependent Entity
An entity is called "Dependent" or "Weak" if it
inherits part of its identifier from another entity. A simple example is
the sales order line which might be identified by a sales order number,
inherited by a dependent relationship to the sales order, plus a sales
order line number local to the dependent entity. In this example, the
line number alone is hardly unique, since every sales order will have a
line number 1 (and perhaps many more). But the combination of the sales
order number plus the sales order line number make each line
unique.
In a conceptual or logical data model, an entity represents
a container or holder of data concepts; i.e., the object which we wish
to describe or record. Entities are created in the CDM with the tool box
entity icon.
PowerDesigner has an extensive facility for defining "business
rules" and attaching them to almost any modeled object. Rules can
be free-form text or tightly coded program code targeted at the client
workstation or the server DBMS engine.
The zoom
icon
it links to documents where the defined term is used.