The ERA Data Model: Entities, Relations and Attributes
Relational Algebra
Validating a Relation Instance
Entities and Classes
Entity Sets as Tables
Relations are Sets of Points
Dimension or Arity
Role and Multiplicity
Multiplicity (1)
Multiplicity Notations
Mincard:MaxCard Notation (1)
Mincard:MaxCard Notation (2)
UML vs CDIF Notation (Multiplicity vs. Cardinality)
UML or CDIF: Which is better?
Multiplicity vs. Cardinality
Multiplicity (2)
Entities have ‘Roles’ in Relations
Relations as Characteristic Functions
Example of MVF and CFR:
CFR as a Database Query
Advantages of Characteristic Function Representation:
Primary Keys as Indices
Partial vs. Total Relations
Relations Are Multi-valued
Sparse Matrix Representation
Directed Graph Example
Binary Relations as Subsets
Structured or Composite Data Types as Relations
Relation Implementation
Pkeys and fkeys
Organization of VMNetDB
Tables in VMNetDB
Super-to-Subclass or Gen-Spec Relations
Schemas from ERA Diagrams
Parent and Child Roles
Drawing Relations:
Inheritance Relations
Gen-Spec Relation Notation
Notation for Inheritance
Reflective databases:
Metatables TT and TA
Schemas and Gencpp
Intension vs. Extension
Example (Tree Schema SU->WH->IT)
Schema as Drawn by BDE
Schema produced by b2t + t2s:
Struct declared by chgen:
MetaSchema Tables TT and TA
Meta-tables TT, TA are Self-Describing:
Merging Sub-schemas
Constraints on Schema Unions
Compression (Breadth-First)
Compression (Depth-First)
Email: lechner@cs.uml.edu
Home Page: www.cs.uml.edu/~lechner
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