Entity Relationship Diagram
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An entity relationship diagram (ERD) is a representation of data within a domain. It consists of entities as well as relationships between entities.
An
entity can be a tangible, physical object such as a school or student,
or a concept such as a reply or a transaction. Entity can be identified
by extracting objects that are relevant and meaningful to the problem
domain and the system to develop. In entity relationship modeling, the
term entity has synonyms "table", "database table", "entity-type". Yet,
entity is the most commonly used term. Each entity brings along a set of
columns, which are the properties of the entity the attributes belong
to. For instance, entity Student has name, address and grade as columns
(synonyms: attributes, properties, fields). Every entity must have at
least one attribute that can be used to uniquely identify the entity,
which is known as the entity's primary key(s).
Relationships
are capable in linking up entities. Typical examples: one-to-one,
one-to-many, many-to-many. The proper use of relationship is important
in showing HOW entities are related. For instance, one-to-many
relationship must be used for modeling the fact that 'one school has
many students'.
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Entity Relationship Diagram
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Synchronization with Class Diagram
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ERD Sample
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An entity relationship diagram showing the entities of a simple order processing system. |
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ERD notations
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Here
are the notations supported by ERD: Entity, database view, sequence,
one-to-one relationship, one-to-many relationship, many-to-many
relationship, stored procedure, stored procedure resultset, triggers. |
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Conceptual ERD
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Conceptual
ERD outline the primary entities/components of proposed system by
drawing a high level design. It is developed by based on the
requirements for the system/application to ne developed. |
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Logical ERD
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Logical ERD refines conceptual design to include/exclude primary entities and relate them. |
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Physical ERD
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The most detailed design that is readily adaptable to physical database. |
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Database-specific column types
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An
entity (database table) is formed by number of columns which represents
the attributes or properties of that entity. Each column contains a
column type, which is the type of that property. For example, a column
age have type integer. Visual Paradigm supports a number of database
types. When you switch between database types, the column types will be
updated accordingly, to adopt the new database selection. Here is a list
of supported database type: MySQL, MS SQL Server, Oracle, HSQL, Sybase ASE, Sybase SQL Anywhere, PostgreSQL, Cloudscape/Derby, DB2, Ingres, OpenEdge, Informix, Firebird, FrontBase, Cache, SQLite, H2. |
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Related Links
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Know-How - Compare databases with Visual Diff |
http://knowhow.visual-paradigm.com/?p=421 |
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Know-How - Model sub-type in ERD |
http://knowhow.visual-paradigm.com/?p=563 |
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DB Visual ARCHITECT (DB-VA) |
http://www.visual-paradigm.com/product/dbva/ |
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Tutorials of DB Visual ARCHITECT (DB-VA) |
http://www.visual-paradigm.com/product/dbva/tutorials.jsp |
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Entity Relationship Diagram
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Synchronization with Class Diagram
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