Er modelling using uml
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This document provides an overview of entity-relationship (ER) modeling concepts and techniques. It describes how to identify entities, attributes, relationships and draw ER diagrams. It also discusses identifying and resolving problems in ER models called connection traps, such as fan traps and chasm traps. The goal is to build an accurate ER model from requirements to design a relational database without logical inconsistencies.
Er modelling using uml
- 1. Chapter 11 Entity-Relationship modeling Transparencies 息 Pearson Education Limited 1995, 2005
- 2. Chapter 11 - Objectives How to use EntityRelationship (ER) modeling in database design. Basic concepts associated with ER model. Diagrammatic technique for displaying ER model using Unified Modeling Language (UML). How to identify and resolve problems with ER models called connection traps. How to build an ER model from a requirements 2 息 Pearson Education Limited 1995, 2005 specification.
- 3. ER diagram of Branch user views of DreamHome 息 Pearson Education Limited 1995, 2005 3
- 4. Concepts of the ER Model Entity types Relationship types Attributes 息 Pearson Education Limited 1995, 2005 4
- 5. Entity Type Entity type Group of objects with same properties, identified by enterprise as having an independent existence. Entity occurrence Uniquely identifiable object of an entity type. 息 Pearson Education Limited 1995, 2005 5
- 6. Examples of Entity Types 息 Pearson Education Limited 1995, 2005 6
- 7. ER diagram of Staff and Branch entity types 息 Pearson Education Limited 1995, 2005 7
- 8. Relationship Types Relationship type Set of meaningful associations among entity types. Relationship occurrence Uniquely identifiable association, which includes one occurrence from each participating entity type. 息 Pearson Education Limited 1995, 2005 8
- 9. Semantic net of Has relationship type 息 Pearson Education Limited 1995, 2005 9
- 10. ER diagram of Branch Has Staff relationship 息 Pearson Education Limited 1995, 2005 10
- 11. Relationship Types Degree of a Relationship Number of participating entities in relationship. Relationship of degree : two is binary three is ternary four is quaternary. 息 Pearson Education Limited 1995, 2005 11
- 12. Binary relationship called POwns 息 Pearson Education Limited 1995, 2005 12
- 13. Ternary relationship called Registers 息 Pearson Education Limited 1995, 2005 13
- 14. Quaternary relationship called Arranges 息 Pearson Education Limited 1995, 2005 14
- 15. Relationship Types Recursive Relationship Relationship type where same entity type participates more than once in different roles. Relationships may be given role names to indicate purpose that each participating entity type plays in a relationship. 息 Pearson Education Limited 1995, 2005 15
- 16. Recursive relationship called Supervises with role names 息 Pearson Education Limited 1995, 2005 16
- 17. Entities associated through two distinct relationships with role names 息 Pearson Education Limited 1995, 2005 17
- 18. Attributes Attribute Property of an entity or a relationship type. Attribute Domain Set of allowable values for one or more attributes. 息 Pearson Education Limited 1995, 2005 18
- 19. Attributes Simple Attribute Attribute composed of a single component with an independent existence. Composite Attribute Attribute composed of multiple components, each with an independent existence. 息 Pearson Education Limited 1995, 2005 19
- 20. Attributes Single-valued Attribute Attribute that holds a single value for each occurrence of an entity type. Multi-valued Attribute Attribute that holds multiple values for each occurrence of an entity type. 息 Pearson Education Limited 1995, 2005 20
- 21. Attributes Derived Attribute Attribute that represents a value that is derivable from value of a related attribute, or set of attributes, not necessarily in the same entity type. 息 Pearson Education Limited 1995, 2005 21
- 22. Keys Candidate Key Minimal set of attributes that uniquely identifies each occurrence of an entity type. Primary Key Candidate key selected to uniquely identify each occurrence of an entity type. Composite Key A candidate key that consists of two or more attributes. 息 Pearson Education Limited 1995, 2005 22
- 23. ER diagram of Staff and Branch entities and their attributes 息 Pearson Education Limited 1995, 2005 23
- 24. Entity Type Strong Entity Type Entity type that is not existence-dependent on some other entity type. Weak Entity Type Entity type that is existence-dependent on some other entity type. 息 Pearson Education Limited 1995, 2005 24
- 25. Strong entity type called Client and weak entity type called Preference 息 Pearson Education Limited 1995, 2005 25
- 26. Relationship called Advertises with attributes 息 Pearson Education Limited 1995, 2005 26
- 27. Structural Constraints Main type of constraint on relationships is called multiplicity. Multiplicity - number (or range) of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type through a particular relationship. Represents policies (called business rules) established by user or company. 息 Pearson Education Limited 1995, 2005 27
- 28. Structural Constraints The most common degree for relationships is binary. Binary relationships are generally referred to as being: one-to-one (1:1) one-to-many (1:*) many-to-many (*:*) 息 Pearson Education Limited 1995, 2005 28
- 29. Semantic net of Staff Manages Branch relationship type 息 Pearson Education Limited 1995, 2005 29
- 30. Multiplicity of Staff Manages Branch (1:1) relationship 息 Pearson Education Limited 1995, 2005 30
- 31. Semantic net of Staff Oversees PropertyForRent relationship type 息 Pearson Education Limited 1995, 2005 31
- 32. Multiplicity of Staff Oversees PropertyForRent (1:*) relationship type 息 Pearson Education Limited 1995, 2005 32
- 33. Semantic net of Newspaper Advertises PropertyForRent relationship type 息 Pearson Education Limited 1995, 2005 33
- 34. Multiplicity of Newspaper Advertises PropertyForRent (*:*) relationship 息 Pearson Education Limited 1995, 2005 34
- 35. Structural Constraints Multiplicity for Complex Relationships Number (or range) of possible occurrences of an entity type in an n-ary relationship when other (n-1) values are fixed. 息 Pearson Education Limited 1995, 2005 35
- 36. Semantic net of ternary Registers relationship with values for Staff and Branch entities fixed 息 Pearson Education Limited 1995, 2005 36
- 37. Multiplicity of ternary Registers relationship 息 Pearson Education Limited 1995, 2005 37
- 38. Summary of multiplicity constraints 息 Pearson Education Limited 1995, 2005 38
- 39. Structural Constraints Multiplicity is made up of two types of restrictions on relationships: cardinality and participation. 息 Pearson Education Limited 1995, 2005 39
- 40. Structural Constraints Cardinality Describes maximum number of possible relationship occurrences for an entity participating in a given relationship type. Participation Determines whether all or only some entity occurrences participate in a relationship. 息 Pearson Education Limited 1995, 2005 40
- 41. Multiplicity as cardinality and participation constraints 息 Pearson Education Limited 1995, 2005 41
- 42. Problems with ER Models Problems may arise when designing a conceptual data model called connection traps. Often due to a misinterpretation of the meaning of certain relationships. Two main types of connection traps are called fan traps and chasm traps. 息 Pearson Education Limited 1995, 2005 42
- 43. Problems with ER Models Fan Trap Where a model represents a relationship between entity types, but pathway between certain entity occurrences is ambiguous. Chasm Trap Where a model suggests the existence of a relationship between entity types, but pathway does not exist between certain entity occurrences. 息 Pearson Education Limited 1995, 2005 43
- 44. An Example of a Fan Trap 息 Pearson Education Limited 1995, 2005 44
- 45. Semantic Net of ER Model with Fan Trap At which branch office does staff number SG37 work? 息 Pearson Education Limited 1995, 2005 45
- 46. Restructuring ER model to remove Fan Trap 息 Pearson Education Limited 1995, 2005 46
- 47. Semantic Net of Restructured ER Model with Fan Trap Removed SG37 works at branch B003. 息 Pearson Education Limited 1995, 2005 47
- 48. An Example of a Chasm Trap 息 Pearson Education Limited 1995, 2005 48
- 49. Semantic Net of ER Model with Chasm Trap At which branch office is property PA14 available? 息 Pearson Education Limited 1995, 2005 49
- 50. ER Model restructured to remove Chasm Trap 息 Pearson Education Limited 1995, 2005 50
- 51. Semantic Net of Restructured ER Model with Chasm Trap Removed 息 Pearson Education Limited 1995, 2005 51