COMPSCI 122A Lecture Notes - Lecture 2: Unique Key, Data Integrity, Compound Key
6 Apr 2017
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Conceptual design: (er model used at this stage) What information about these entities and relationships should we store in the database. A database schema in the er model can be represented pictorially. Entity - real-world object, distinguishable from all other objects, an entity is described (in db-land) using a set of attributes. Entity set: a collection of similar entities. All entities in an entity set have the same set of attributes. (until we get to. Each entity set has a key (a unique identifier); this can be either one attribute (an atomic key) or several attributes (called a composite key ) Each attribute has a domain (similar to a data type) Relationships: association among two or more entities, eg, santa claus works in the toy department. An n-ary relationships set r relates n entity sets e1 en; each relationship in r involves entities e1:e1, , en:en. One entity set can participate in different relationship sets - or in different.
