chapter 3 the enhanced e-r model

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Chapter 3The Enhanced E-R Model

Jason C. H. Chen, Ph.D.Professor of MIS

School of Business AdministrationGonzaga UniversitySpokane, WA 99258chen@gonzaga.edu

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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

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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.

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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.

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PARADIGMS(Definition)

• A paradigm is a way of viewing things and thinking about things.

L

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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

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Figure 3-1 Basic notation for supertype/subtype notation

a) EER notation

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Different modeling tools may have different notation for the same modeling constructs

b) Microsoft

Visio Notation

Figure 3-1 Basic notation for supertype/subtype notation (cont.)

b) Microsof

t Visio Notation

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All employee subtypes will have employee number, name, address, and date-hired

Each employee subtype will also have its own attributes

Fig. 3-2: Employee supertype with three subtypes

is_a GeneralizationSpecializationhas_a

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Object-Oriented Design

What is the difference with ERM?(see next slide)

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Attributes Operations/ behavior/ methods

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

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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 ______ values of all attributes of the supertype.

• An occurrence of a subtype is also an occurrence of the supertype

inherit

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Figure 3-3 - Relationships in a hospital. Is it appropriate?

What is the cardinality between “Patient” and “Bed”?

Assign

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Figure 3-3 - Relationships in a hospital. Is it appropriate?

Why optional?

Is this cardinatly (“optional one” or “mandatory one”) appropriate?

Does “every” PATIENT need a BED?

AssignWhy mandatory?

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Figure 3-3 - Relationships in a hospital. Is it appropriate?

Why optional?

Is this cardinatly (“optional one” or “mandatory one”) appropriate?

Does “every” PATIENT need a BED?

AssignWhy optional?

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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

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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)

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Figure 3-4 Example of generalization

a) Three entity types: CAR, TRUCK, and MOTORCYCLE

All these types of vehicles have common attributes

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Figure 3-4 Example of generalization (cont.)

So we put the shared attributes in a supertype

Note: no subtype for motorcycle, since it has no unique attributes

b) Generalization to VEHICLE supertype

MOTORCYCLE WAGON

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Figure 3-5 Example of specialization

a) Entity type PART

Only applies to manufactured parts

Applies only to purchased parts

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b) Specialization to MANUFACTURED PART and PURCHASED PART

Figure 3-5 Example of specialization (cont.)

Created 2 subtypes

Note: multivalued attribute was replaced by an associative entity relationship to another entity

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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)

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

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b) Partial specialization ruleFigure 3-6 Examples of completeness constraints (cont.)

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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

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a) Disjoint rule

Figure 3-7 Examples of disjointness constraints

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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

Figure 3-7 Examples of disjointness constraints (cont.)

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b) Overlap rule

Figure 3-7 Examples of disjointness constraints (cont.)

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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)

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Figure 3-8 Introducing a subtype discriminator (disjoint rule)

Implementation:C++: switch(Employee_Type){ case ’C’:..}

SQL:IF/THEN/ELSE

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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

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Figure 3-10 Example of supertype/subtype hierarchy

?

Commonattributes for all levels

Inherit all attributes from all supertypes

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Break ! (Ch. 3 - Part I)In class exercise:#9, 10 (p. 114)

HW - #8 (p.114)- turn in a hardcopy

using “Visio”/Word- Revise your MVC

ER/M

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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

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Figure 3-11 E-R diagram for Pine Valley Furniture Company

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Figure 3-12 EER diagram for Pine Valley Furniture Company using Microsoft Visio

Related groups of entities could become clusters

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Related groups of entities could become clusters

Figure 3-12 (revised) EER diagram for Pine Valley Furniture Company using Microsoft Visio

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Figure 3-12 (revised) EER diagram of PVF entity clusters

More readable, isn’t it?

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Figure 3-12 (revised) Manufacturing entity cluster

Detail for a single cluster

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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”)

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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

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MVC_Hospital HWPhase 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 42. 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.

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MVC_Hospital

Phase II. (a) a script file (MVC_PhaseII_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.txt Upload both *.sql and *.txt files to the Bb. Turn in ONLY spooled file. (*.txt)

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.txt. 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 both *.sql and *.txt files to the Bb. Turn in only spooled file (*.txt)