ISM 6128 Final Study Guide.docx

ISM 6128 Final Study Guide.docx - ISM 6128 Final...

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ISM 6128 Final Structuring System Data Requirements Entity-relationship data model (E-R model): A detailed, logical representation of the entities, associations, and data elements for an organization or business area. Entity type: A collection of entities that share common properties or characteristics. Given a singular name. Entity instance: A single occurrence of an entity type. Also known as an instance. Attribute: A named property or characteristic of an entity that is of interest to the organization. Required- must have a value for every entity instance Optional- may not have a value for every entity instance Composite- has meaningful component parts Multivalued attribute: An attribute that may take on more than one value for each entity instance. Ex: employee skill attribute, each employee can and probably will have more than 1 skill Repeating group: A set of two or more multivalued attributes that are logically related. Derived attribute: An attribute whose value can be computed from related attribute values. Candidate key: An attribute (or combination of attributes) that uniquely identifies each instance of an entity type. Particular combinations are not repeated in different rows Identifier (primary key): A candidate key that has been selected as the unique, identifying characteristic for an entity type. Relationship: An association between the instance of one or more entity types that is of interest to the organization. Degree of relationship: number of entity types that participate in the relationship o Unary : A relationship between instances of one entity type; also called recursive relationship .
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