Search results
Results from the WOW.Com Content Network
Chen's notation for entity–relationship modeling uses rectangles to represent entity sets, and diamonds to represent relationships appropriate for first-class objects: they can have attributes and relationships of their own. If an entity set participates in a relationship set, they are connected with a line.
In systems analysis, a one-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model). For example, take a car and an owner of the car. The car can only be owned by one owner at a time or not owned at all, and an owner could own zero, one, or multiple cars.
An associative entity is a term used in relational and entity–relationship theory. A relational database requires the implementation of a base relation (or base table) to resolve many-to-many relationships. A base relation representing this kind of entity is called, informally, an associative table. An associative entity (using Chen notation)
The data structure diagrams is a predecessor of the entity–relationship model (E–R model). In DSDs, attributes are specified inside the entity boxes rather than outside of them, while relationships are drawn as boxes composed of attributes which specify the constraints that bind entities together. DSDs differ from the E–R model in that ...
Example of an IDEF1X diagram. Integration DEFinition for information modeling (IDEF1X) is a data modeling language for the development of semantic data models.IDEF1X is used to produce a graphical information model which represents the structure and semantics of information within an environment or system.
An example model showing the different graphical symbols for all the concepts can be seen below. The symbols resemble those used in entity–relationship modeling, with a couple of extensions. A double outline on an attribute or tie indicates that a history of changes is kept.
Chen is one of the pioneers of using entity–relationship concepts in software and information system modeling and design. Before Chen's paper, the basic entity–relationship ideas were used mostly informally by practitioners. Chen first published an abstract and presented his ER model in the First Very Large Database Conference in September ...
Object–role models are based on elementary facts, and expressed in diagrams that can be verbalised into natural language. A fact is a proposition such as "John Smith was hired on 5 January 1995" or "Mary Jones was hired on 3 March 2010".