Developing an IT Application Using Advantage:Gen  Data Modeling: I-bars and subtypes

Data Analysis u What information is required by the business u Logical view vs. physical view u Carried out in parallel with activity analysis

Composite Identifier Using an Attribute and Relationship Order Item Order I is included on includes Attributes ITEM NUMBER PRICE QUANTITY Identifier is a combination of: ITEM NUMBER and the fact that Each ORDER ITEM is included on one ORDER

Composite Identifier Using Relationships ProductWarehouse Stock Item IooI holds is held for is stored in stores Identifier is a combination of: Each STOCK ITEM is stored in one WAREHOUSE and each STOCK ITEM holds one PRODUCT

Entity Subtypes u An subtype is a subdivision of the entity supertype u Each subtype must have one or more special attributes of its own and/or participate in one or more special relationship of its own u The special attributes and relationships are not common to all instances of the entity

Partitioning u A basis for subdividing instances of an entity supertype into subtypes. A subtype can in turn have partitionings of its own. u A classifying attribute is the basis for partitioning, e.g. EMPLOYEE - Name, Number, Type where Type can be Full-Time or Part-Time u Each subtype must be associated with a permitted value of the classifying attribute u Each subtype inherits properties ( attributes, identifiers, relationships) of its parent entity

Partitioning can be u There can be multiple partitionings EmployeeManager Staff Full Time Part Time NAME ADDRESS NUMBER TYPE JOB STATUS

Rules for Partitioning and Subtypes u Each subtype belongs to exactly one partitioning u Each partitioning must be associated with a classifying attribute u The subtype to which a given entity occurrence belongs must be identifiable by a classifying attribute value u A fully enumerated partitioning must divide the entity type into two or more subtypes