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Chapter 3 The Enhanced E-R Model

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1 Chapter 3 The Enhanced E-R Model
Jason C. H. Chen, Ph.D. Professor of MIS School of Business Administration Gonzaga University Spokane, WA 99258

2 Objectives Define terms
Understand use of supertype/subtype relationships Understand use of specialization and generalization techniques Specify completeness and disjointness constraints Develop supertype/subtype hierarchies for realistic business situations Develop entity clusters Explain universal (packaged) data model Describe special features of data modeling project using packaged data model

3 What is the Enhanced E-R Model (EE-R Model) and Why?
The Enhanced E-R model (EE-R) is an extended E-R model with new modeling constructs. Why the EE-R model? The business environment has changed dramatically. Business relationships and data are more complex.

4 Business Rules The EE-RD are used to capture important business rules such as constraints in supertype/sbubtype relationship. The rules automatically become constraints that are forced by the DBMS and are used to maintain the organizational database in a consistent and valid state.

5 PARADIGMS (Definition)
A paradigm is a way of viewing things and thinking about things. L

6 Supertypes and Subtypes
Subtype: A subgrouping of the entities in an entity type which has attributes that are distinct from those in other subgroupings Supertype: An generic entity type that has a relationship with one or more subtypes (Fig. 3-1, 2) Inheritance: Subtype entities inherit values of all attributes of the supertype An instance of a subtype is also an instance of the supertype

7 Figure 3-1 Basic notation for supertype/subtype notation
a) EER notation

8 Figure 3-1 Basic notation for supertype/subtype notation (cont.)
b) Microsoft Visio Notation b) Microsoft Visio Notation Different modeling tools may have different notation for the same modeling constructs

9 is_a Fig. 3-2: Employee supertype with three subtypes Generalization
All employee subtypes will have employee number, name, address, and date-hired is_a Generalization Specialization has_a Each employee subtype will also have its own attributes


11 Attributes Operations/ behavior/ methods

12 UML notation: An example of Object-Oriented (O-O) Approach

13 Relationships and Subtypes
Relationships at the supertype level indicate that all subtypes will participate in the relationship The instances of a subtype may participate in a relationship unique to that subtype. In this situation, the relationship is shown at the subtype level (Fig. 3-3) Subtype entities inherit values of all attributes of the supertype. An occurrence of a subtype is also an occurrence of the supertype

14 Figure 3-3 - Supertype/subtype relationships in a hospital
Both outpatients and resident patients are cared for by a responsible physician Only resident patients are assigned to a bed

15 Generalization and Specialization
Generalization: The process of defining a more general entity type from a set of more specialized entity types. BOTTOM-UP (Fig. 3-4) Specialization: The process of defining one or more subtypes of the supertype, and forming supertype/subtype relationships. TOP-DOWN (Fig. 3-5)

16 Figure 3-4 Example of generalization
a) Three entity types: CAR, TRUCK, and MOTORCYCLE All these types of vehicles have common attributes

17 Figure 3-4 Example of generalization (cont.)
b) Generalization to VEHICLE supertype So we put the shared attributes in a supertype MOTORCYCLE WAGON Note: no subtype for motorcycle, since it has no unique attributes

18 Figure 3-5 Example of specialization
a) Entity type PART Only applies to manufactured parts Applies only to purchased parts

19 Figure 3-5 Example of specialization (cont.)
b) Specialization to MANUFACTURED PART and PURCHASED PART Note: multivalued attribute was replaced by an associative entity relationship to another entity Created 2 subtypes The same (purchased) part may be purchased from MORE THAN ONE supplier A supplier can SUPPLY more than ONE purchased part.

20 Constraints in Supertype/ Subtype Relationships
Completeness Constraints: Whether an instance of a supertype must also be a member of at least one subtype. Total Specialization Rule: Yes (Fig. 3-6a - double line convention) Partial Specialization Rule: No (Fig. 3-6b - single line convention)

21 Figure 3-6 Examples of completeness constraints
a) Total specialization rule

22 Figure 3-6 Examples of completeness constraints (cont.)
b) Partial specialization rule

23 Constraints in Supertype/ Disjointness constraint
Disjointness Constraints: Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes. Disjoint Rule: An instance of the supertype can be only ONE of the subtypes Overlap Rule: An instance of the supertype could be more than one of the subtypes

24 Figure 3-7 Examples of disjointness constraints
a) Disjoint rule

25 Figure 3-7 Examples of disjointness constraints (cont.)
b) Overlap rule A part may be both a Purchased Part and a Manufactured Part at the same time, but must be one or the other due to Total Specialization

26 Figure 3-7 Examples of disjointness constraints (cont.)
b) Overlap rule

27 Constraints in Supertype/ Subtype Discriminators
Subtype Discriminator: An attribute of the supertype whose values determine the target subtype(s) Disjoint – a simple attribute with alternative values to indicate the possible subtypes (Fig. 3-8) Overlapping – a composite attribute whose subparts pertain to different subtypes. Each subpart contains a boolean value to indicate whether or not the instance belongs to the associated subtype (Fig. 3-9) Summary Example (Fig. 3-10)

28 Figure 3-8 Introducing a subtype discriminator (disjoint rule)
Implementation: C++: switch(Employee_Type) { case ’C’: .. } SQL: IF/THEN/ELSE

29 Figure 3-9 Subtype discriminator (overlap rule)
A composite attribute with sub-attributes indicating “yes” or “no” or both (“yes” and “no”) to determine whether it is of each subtype

30 ? Figure 3-10 Example of supertype/subtype hierarchy Common
attributes for all levels ? Inherit all attributes from all supertypes

31 Break ! (Ch. 3 - Part I) In class exercise: #12, 13 (p. 143-144) HW
turn in a hardcopy using “Visio”/Word Revise your MVC ER/M

32 Entity Clusters EER diagrams are difficult to read when there are too many entities and relationships Solution: group entities and relationships into entity clusters Entity cluster: set of one or more entity types and associated relationships grouped into a single abstract entity type

33 Figure 3-13a Possible entity clusters for Pine Valley Furniture in Microsoft Visio
Related groups of entities could become clusters

34 Figure 3-13b EER diagram of PVF entity clusters
More readable, isn’t it?

35 Figure 3-14 Manufacturing entity cluster
Detail for a single cluster

36 Packaged Data Models Predefined data models
Could be universal or industry-specific Universal data model = a generic or template data model that can be reused as a starting point for a data modeling project (also called a “pattern”)

37 Advantages of Packaged Data Models
Use proven model components Save time and cost Less likelihood of data model errors Easier to evolve and modify over time Aid in requirements determination Easier to read Supertype/subtype hierarchies promote reuse Many-to-many relationships enhance model flexibility Vendor-supplied data model fosters integration with vendor’s applications Universal models support inter-organizational systems

38 Figure 3-15 PARTY, PARTY ROLE, and ROLE TYPE in a universal data model
(a) Basic PARTY universal data model Packaged data models are generic models that can be customized for a particular organization’s business rules

39 Figure 3-15 PARTY, PARTY ROLE, and ROLE TYPE in a universal data model
(b) PARTY supertype/subtype hierarchy

40 Figure 3-16 Extension of a universal data model to include PARTY RELATIONSHIPS

41 Phase I - Logical Design Phase
MVC_Hospital HW Phase I - Logical Design Phase Draw a entity-relationship diagram (enterprise model) for Mountain View community Hospital, based on the narrative description of the case and this handout (but the entities are from the five (5) figures/reports shown above). You should create a file and turn in with a hardcopy (called MVC_PhaseI_ERD_Lname_Fname.docx) contains the following materials: 1. Read and employ materials from chapters 3 and 4 2. Include entities, associations (with detail multiplicity), and attributes. 3. Determine and draw the order of entering data Next phase -- implementation, create SQL script file for table structure and data base (values). Upload ONLY the .docx file to the Bb.

42 MVC_Hospital Phase II. Phase III. Create two script files:
(a) a script file (MVC_Hospital_Lastname_Firstname.SQL) that contains a set of commands of DROP, CREATE, and INSERT that performs the same functions as in the script file of Northwoods.sql (b) Save your spooled file (both script file and result from SQL) as MVC_PhaseII_Spool_Lastname_Firstname.LST Upload the spooled file to the Bb. Phase III. (a) Second script file (MVC_PhaseIII_QUERIES_Lastname_Firstname.SQL) containing a set of SQL commands that answer the questions. Test the query one/time successfully. Note that you may need other SQL commands and create database views for the purpose of answering questions easily. You may need to read other references related the SQL from the text book (e.g., Chapters 6 & 7 of the main text). (b) Save the spooled file as MVC_PhaseIII_Spool_Lastname_Firstname.LST. Finally, you create a new file (*.docx) containing all work done from Parts I, II and save them in the file MVC_Hospital_Complete_Lastname_Firstname.docx. (c) The file should contain your class and personal information, information for each question (re-type with question number) as well as each individual query and result. Upload ONLY the .docx file to the Bb.

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