By Herbert J.
Bernstein
© Copyright 2000, 2002 Herbert J. Bernstein
Data Modeling is the term used for a variety of techniques used
to develop models of information systems which will provide a framework
within which to develop information systems and processes. It focuses on
what information is moved and where. It is one of
many possible approaced to modeling a system. Here we will compare it
to physical models and logical models
- Physical Model
- Labeling (conceptual organization) of components of a business system
which preserves the full technical details of how they are implemented.
- e.g. network modeled with physical locations of the nodes and physical
routes of the wires
- Logical Model
- Model in which some portions of the technical detail have been
abstracted
- e.g. network modeled as an anstract graph
- Data Model
- Labeling of the types and instances of information
- See Tim McLellan "Data Modeling: Finding the
Perfect Fit", Dispatch, March / April 1995, Computing
and Network Services, University of Alberta
http://www.islandnet.com/~tmc/html/articles/datamodl.htm
- Static allocation of storage (data structures)
- Dynamic reading and writing of data (data bases)
- Exchanges of data among system components (object orients modeling)
- Entities
- Objects which may originate, accept, hold or process information
- The information associated with an entity is organized as values of attributes
- A set of attributes the values of which uniquely identifies entities are called candidate keys
- A minimal set of of the candidate keys which also uniquely identifies entities may be designated a primary key
- Attributes may be simple or composite or may themselves be objects
- Attributes may be restricted to particular permitted values
- Attributes may have default values
- Relationships
- Associations between objects (or their attributes)
- Bidirectional
- Mandatory or optional
- Named (identified)
- Cardinality
- Practical Data Modeling
- Data organized into tables
- Attributes are column headings
- Values entered into rows
- Some tables are children of other tables
Last Updated on 17 September 2002
By Herbert J. Bernstein
Email: yaya@bernstein-plus-sons.com