Week 3 (Wednesday and Friday)

Week 3 (Wednesday and Friday) - 7/28/2009 SIT103 -...

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7/28/2009 1 SIT103 SIT103 - Introduction Introduction to Database Design Week 3 – lecture 1 Entity-Relationship Modeling Geelong The Entity Relationship (ER) model Entity Relationship Diagrams (ERDs) represent the conceptual database as viewed by the end user ERDs depict the ER model’s three main ERDs depict the ER model s three main components: Entities Attributes Relationships 28 July 2009 2 T2-2009 Entities An entity is represented by a rectangle containing the entity’s name It is usually written in capital letters, and is a noun Corresponds to a table and not to a row in the relational environment 28 July 2009 3 T2-2009
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7/28/2009 2 Attributes Composite attribute – can be further subdivided Simple attribute cannot be further subdivided Single-valued attribute – can only have a single value Multi-valued attributes – can have many values A single-valued attribute is not necessarily a simple attribute 28 July 2009 4 T2-2009 Attributes (cont.) A Composite Attribute – STU_NAME can be subdivided into these three simple attributes Single-Value Attribute Simple Attribute ? Entity 5 Domains Attributes have a domain : set of possible values Attributes may share a domain 28 July 2009 6 T2-2009
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7/28/2009 3 Primary keys y Underlined in the ER diagram y Key attributes are also underlined in frequently used table structure shorthand Ideally composed of only a single attribute Possible to use a composite key , i.e., primary key composed of more than one attribute 28 July 2009 7 T2-2009 Multi ulti-valued attribute valued attribute A double line denotes a multi-valued attribute Underlined attribute is a key 8 Multi Multi-valued valued attribute attribute (cont.) y Can lead to problems y You should avoid them in implementation Create new attributes, one for each of the original multi-valued attribute’s components Create a new entity composed of original Create a new entity composed of original multi-valued attribute’s components 28 July 2009 9 T2-2009
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7/28/2009 4 Example 10 Another example 11 Derivable attributes y Attribute whose value may be calculated
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This note was uploaded on 09/27/2009 for the course SEB 323 - S taught by Professor Professor during the Three '09 term at Deakin.

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Week 3 (Wednesday and Friday) - 7/28/2009 SIT103 -...

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