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High-level conceptual model Used for the conceptual design of DB

applications Many DB design tools employs its concepts

Chen 1976 -- MIT “The Entity-Relationship Model -- Toward a Unified

View of Data” ACM - TODS

Chapter 3Data Modeling Using the Entity-Relationship Model

p 43 2

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Overview of Database Design Process Two main activities:

Database design Applications design

Focus in this chapter on database design To design the conceptual schema for a database

application Applications design focuses on the programs and

interfaces that access the database Generally considered part of software engineering

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Entities, Attributes

Entity - a ”thing” in the real world with independent existence

Attribute - properties that describe the entity Simple (atomic) vs. composite Single-values vs. multivalued Stored vs. derived Null values Complex Attributes

{AddressPhone({Phone(areacode,phonenumber)}, Address(StreetAddress(Number,Street,AptNumber),City,State,Zip))}

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Entity Types, Entity Set, Keys, and Value Sets

Entity Types: Defines a collection (or set) of entities that have the same attributes

e.g. employee, student

Entity Set: The collections of all entities of a particular entity type

e.g. employee = set of all employees

Value Sets: specifies the set of values assigned to attribute (domain of values)

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1) Existence Dependency X and Y are entities Y entity cannot exist without X entity

Y cannot enter the database unless its corresponding X is there

if X is dropped from the database, Y must be dropped as well

X = strong, parent, owner, dominant Y = weak, child, dependent, subordinate

Dependencies

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Weak Entity Types An entity that does not have a key attribute A weak entity must participate in an identifying relationship

type withan owner or identifying entity type Entities are identified by the combination of:

A partial key of the weak entity type The particular entity they are related to in the identifying

entity type Example:

A DEPENDENT entity is identified by the dependent’s first name, and the specific EMPLOYEE with whom the dependent is related

Name of DEPENDENT is the partial key DEPENDENT is a weak entity type EMPLOYEE is its identifying entity type via the identifying relationship type DEPENDENT_OF

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2) Identifier Dependency Occurs when the weak entity set does not have

a candidate key, and its instances are indistinguishable w/o a relationship with other

entity (e.g. grade).

3) Referential Dependency Occurs when a weak entity contains a foreign

key of the corresponding strong entity (e.g. essn in Dependent table)

Referential Constraint A nonnull value of the foreign key attribute in the entity

instance must always equal the value of the primary key of an associated strong entity instance.

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Many-to-one (N:1) Relationship

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Many-to-many (M:N) Relationship

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Displaying a recursive relationship In a recursive relationship type.

Both participations are same entity type in different roles.

For example, SUPERVISION relationships between EMPLOYEE (in role of supervisor or boss) and (another) EMPLOYEE (in role of subordinate or worker).

In following figure, first role participation labeled with 1 and second role participation labeled with 2.

In ER diagram, need to display role names to distinguish participations.

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A Recursive Relationship Supervision`

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Recursive Relationship Type is: SUPERVISION(participation role names are shown)

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Notation for Constraints on Relationships Cardinality ratio (of a binary relationship): 1:1,

1:N, N:1, or M:N Shown by placing appropriate numbers on the

relationship edges. Participation constraint (on each participating

entity type): total (called existence dependency) or partial. Total shown by double line, partial by single line.

NOTE: These are easy to specify for Binary Relationship Types.

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Alternative (min, max) notation for relationship structural constraints: Specified on each participation of an entity type E in a relationship

type R Specifies that each entity e in E participates in at least min and at

most max relationship instances in R Default(no constraint): min=0, max=n (signifying no limit) Must have minmax, min0, max 1 Derived from the knowledge of mini-world constraints Examples:

A department has exactly one manager and an employee can manage at most one department.

Specify (0,1) for participation of EMPLOYEE in MANAGES Specify (1,1) for participation of DEPARTMENT in MANAGES

An employee can work for exactly one department but a department can have any number of employees.

Specify (1,1) for participation of EMPLOYEE in WORKS_FOR Specify (0,n) for participation of DEPARTMENT in WORKS_FOR

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The (min,max) notation for relationship constraints

Read the min,max numbers next to the entity type and looking away from the entity type

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COMPANY ER Schema Diagram using (min, max) notation

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Alternative diagrammatic notation

ER diagrams is one popular example for displaying database schemas

Many other notations exist in the literature and in various database design and modeling tools

Appendix A illustrates some of the alternative notations that have been used

Unified Modeling Language (UML) class diagrams is representative of another way of displaying ER concepts that is used in several commercial design tools

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Summary of notation for ER diagrams

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Unified Modeling Language (UML) class diagrams Represent classes (similar to entity types) as large rounded

boxes with three sections: Top section includes entity type (class) name Second section includes attributes Third section includes class operations (operations are not in

basic ER model) Relationships (called associations) represented as lines

connecting the classes Other UML terminology also differs from ER terminology

Used in database design and object-oriented software design

UML has many other types of diagrams for software design (see Chapter 12)

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UML class diagram for COMPANY database schema

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Other alternative diagrammatic notations

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Relationships of Higher Degree Relationship types of degree 2 are called binary Relationship types of degree 3 are called ternary

and of degree n are called n-ary In general, an n-ary relationship is not equivalent

to n binary relationships Constraints are harder to specify for higher-

degree relationships (n > 2) than for binary relationships

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Discussion of n-ary relationships (n > 2) In general, 3 binary relationships can represent different

information than a single ternary relationship (see Figure 3.17a and b on next slide)

If needed, the binary and n-ary relationships can all be included in the schema design (see Figure 3.17a and b, where all relationships convey different meanings)

In some cases, a ternary relationship can be represented as a weak entity if the data model allows a weak entity type to have multiple identifying relationships (and hence multiple owner entity types) (see Figure 3.17c)

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Example of a ternary relationship

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Discussion of n-ary relationships (n > 2) If a particular binary relationship can be derived

from a higher-degree relationship at all times, then it is redundant

For example, the TAUGHT_DURING binary relationship in Figure 3.18 (see next slide) can be derived from the ternary relationship OFFERS (based on the meaning of the relationships)

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Another example of a ternary relationship

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Displaying constraints on higher-degree relationships The (min, max) constraints can be displayed on the edges –

however, they do not fully describe the constraints Displaying a 1, M, or N indicates additional constraints

An M or N indicates no constraint A 1 indicates that an entity can participate in at most one

relationship instance that has a particular combination of the other participating entities

In general, both (min, max) and 1, M, or N are needed to describe fully the constraints

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Data Modeling Tools A number of popular tools that cover conceptual modeling

and mapping into relational schema design. Examples: ERWin, S- Designer (Enterprise Application Suite),

ER- Studio, etc. POSITIVES:

Serves as documentation of application requirements, easy user interface - mostly graphics editor support

NEGATIVES: Most tools lack a proper distinct notation for relationships with

relationship attributes Mostly represent a relational design in a diagrammatic form

rather than a conceptual ER-based design(See Chapter 12 for details)

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Some of the Currently Available Automated Database Design Tools

COMPANY TOOL FUNCTIONALITY

Embarcadero Technologies

ER Studio Database Modeling in ER and IDEF1X

DB Artisan Database administration, space and security management

Oracle Developer 2000/Designer 2000

Database modeling, application development

Popkin Software

System Architect 2001 Data modeling, object modeling, process modeling, structured analysis/design

Platinum (Computer Associates)

Enterprise Modeling Suite: Erwin, BPWin, Paradigm Plus

Data, process, and business component modeling

Persistence Inc.

Pwertier Mapping from O-O to relational model

Rational (IBM) Rational Rose UML Modeling & application generation in C++/JAVA

Resolution Ltd.

Xcase Conceptual modeling up to code maintenance

Sybase Enterprise Application Suite Data modeling, business logic modeling

Visio Visio Enterprise Data modeling, design/reengineering Visual Basic/C++

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Extended Entity-Relationship (EER) Model (in next chapter) The entity relationship model in its original form

did not support the specialization and generalization abstractions

Next chapter illustrates how the ER model can be extended with Type-subtype and set-subset relationships Specialization/Generalization Hierarchies Notation to display them in EER diagrams

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Chapter Summary ER Model Concepts: Entities, attributes,

relationships Constraints in the ER model Using ER in step-by-step conceptual schema

design for the COMPANY database ER Diagrams - Notation Alternative Notations – UML class diagrams,

others

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Mapping an E-R Model to a Relational Model

1) The entity sets represented by rectangles becomes relations represented by tables

2) For strong entity sets, attributes represented by ovals become attributes of the relations or column headings of the table

For weak entity set - all attributes include all the attributes of the weak entity, plus the primary key of the owner entity

3) The table for a relationship set has column headings consisting of the associated entities, plus column for descriptive attributes if any

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Exercise: create ER-Diagrams

a) COURSE(COURSE#,C_TITLE,INS_NAME,TEXT_BOOK,PUBLISHER)

b) ENROLLMENT(STUID,COURSE#,STUNAME,COURSETITLE, GRADE)

c) PART(PART#,PART_NAME,DEPARTMENT,PRICE)

d) EMPLOYEE(EMPID,EMPNAME,DATE_HIRED,JOB_TITLE, JOB_LEVEL, PROJ#, PROJ_TITLE,DUEDATE,HOURS_WORKED)

 e) BOOK(ISBN,TITLE,AUTHOR,AUTHOR_INSTITUTE,PRICE,

PUBLISHER_NAME, PUBLISHER_ADR)

 f) CUSTOMER(CUSTID,CUSTNAME, PHONE#, STREET,CITY,STATE,ZIP)

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Examples http://www.meds-sdmm.dfo-mpo.gc.ca/me

ds/Prog_Nat/NCIS/Definition/Ncis_ER_diagram.gif

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Data Modeling Tools - Visio 2007

Visio 2007 Demo: Show It Like It Is -- Connect Data to Your Visio Diagram

This demo shows how you can use Microsoft Office Visio Professional 2007 to analyze how a process or other area is actually performing by connecting data to the shapes in your diagram. 1/30/2008Visio 2007 Demo: Create a background and watermark for your drawings

Learn how to create a background and watermark for your drawings in Microsoft Office Visio 2007. 1/25/2008Visio 2007 Demo: Let Data Tell Its Story with Data GraphicsIn this demo, you’ll see how to use data graphics in your Microsoft Office Visio 2007 diagram to present the right data in the right way and to make your points clearly. 1/30/2008

Visio 2007 Demo: Give Your Diagram a Makeover by Applying a Theme

Use themes in Microsoft Office Visio Professional 2007 to easily add color and style to your diagram and create an attractive, engaging piece.1/30/2008Visio 2007 Demo: Get a New Perspective on Data with PivotDiagramsIn this demo, you’ll see how PivotDiagrams can help you get a fresh perspective on your data.

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Oracle Designer – Oracle Designer http://www.oracle.com/technology/

products/designer/demos.htm

Database Design and Generation Creating Entity Diagrams (Viewlet) Creating Database Designs (Viewlet) Working With Server Models (Viewlet) Generating Databases (Viewlet) Capturing Database Designs (Viewlet)

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Data Modeling Tools Sybase – PowerDesigner http://www.sybase.com/products/modelingmetadata/

powerdesigner/demonstrationvideos

http://www.datamodel.org/PowerDesigner/

Database Designers the technical video demonstrates: A Walk Through of a Sample Conceptual Data Model Reverse Engineer a PDM from a Database Iterative Bi-level Design with PowerDesigner Keeping the Modeling and the Servers Synchronized Download this video:

http://download.sybase.com/presentation/pdvideo/pd_dba1.exe