Object Oriented Analysis and Design 1

Chapter 7 Database Design UML Specification for Data Modeling The Relational Data Model and Object Model Persistence Frameworks Database Design

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UML Specification for Data Modeling

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7.1 UML Specification for Data Modeling UML Notation for Data Modeling Modeling Associations in the Data Model Modeling Aggregation in the Data Model Modeling Inheritance in the Data Model

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UML Notation for Data Modeling

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Modeling Associations in the Data Model Associations between two persistent objects

are realized as foreign keys to the associated objects. A foreign key is a column in one table which

contains the primary key value of associated object

Number Course_ID

678 456789

Name Description Number

Math 101 Algebra 456789

Course Offering table

Course tableCourse

- name- description

- number

CourseOffering

- number : String

0..*0..*

1

Primary Key

Foreign Key

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Modeling Aggregation in the Data Model Aggregation is also modeled using foreign

key relationships Using composition implements a cascading

delete constraint

Student.

- studentID : int

Schedule

- semester : Semester

0..*

1

0..*

1

Student_ID Semester

123456 Spring 2001

Schedule table

Student_ID

123456

Foreign Key

Primary Key

Student table

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Modeling Inheritance in the Data Model A data model does not support modeling

inheritance in a direct way Two options

Use separate tables (normalized data) Duplicate all inherited associations and

attributes (de-normalized data)

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Modeling Inheritance in the Data Model - Example

Personname : Stringage : int

CitizenpassportNumber : int

Residentnationality : StringvisaType : String

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Modeling Inheritance in the Data Model - Example

CitizenpassportNumber : SMALLINTperson_ID : SMALLINT

<<PK>> PK_Citizen1()<<FK>> FK_Citizen0()

Personperson_ID : SMALLINTage : SMALLINTname : VARCHAR(32)type : SMALLINT

<<PK>> PK_Person0()<<Unique>> TC_Person0()

0..11 0..11

<<Identifying>>

Residentnationality : VARCHAR(255)visaType : VARCHAR(255)person_ID : SMALLINT

<<PK>> PK_Resident2()<<FK>> FK_Resident1()

0..1

1

0..1

1

<<Identifying>>

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Modeling Inheritance in the Data Model - Example

CitizenpassportNumber : SMALLINTperson_ID : SMALLINTname : VARCHAR(32)age : SMALLINT

<<PK>> PK_Citizen1()<<FK>> FK_Citizen0()

Personperson_ID : SMALLINTage : SMALLINTname : VARCHAR(32)

<<PK>> PK_Person0()<<Unique>> TC_Person0()

0..11 0..11

<<Identifying>>

Residentnationality : VARCHAR(255)visaType : VARCHAR(255)person_ID : SMALLINTname : VARCHAR(32)age : SMALLINT

<<PK>> PK_Resident2()<<FK>> FK_Resident1()

0..1

1

0..1

1

<<Identifying>>

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Modeling Inheritance in the Data Model - Example

Personperson_ID : SMALLINTage : SMALLINTname : VARCHAR(32)type : SMALLINTpassportNumber : SMALLINTnationality : VARCHAR(255)visaType : VARCHAR(255)

<<PK>> PK_Person0()<<Unique>> TC_Person0()

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Modeling Inheritance in the Data Model - Example

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The Relational Data Model and Object Model

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7.2 The Relational Data Model and Object Model The Relational Data Model The Object Model

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The Relational Data Model The relational model is composed of entities and relations.

An entity may be a physical table or a logical projection of several tables also known as a view.

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The Object Model An object model contains classes. Classes define the structure

and behavior of a set of objects, sometimes called objects instances. The structure is represented as attributes (data values) and associations (relationships between classes).

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The Persistence Frameworks

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7.3 Persistence Frameworks The Purpose of a Persistence Framework Hibernate

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The Purpose of a Persistence Framework

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Hibernate Object / Relational mapping (ORM) and persistence /

query framework i.e. It does even more stuff for you!

Some features of Hibernate HibernateDaoSupport – superclass, easy HibernateTemplate access Database independence - sits between the database and your java code,

easy database switch without changing any code Object / Relational Mapping (ORM) - Allows a developer to treat a database

like a collection of Java objects Object oriented query language (HQL) - *Portable* query language,

supports polymorphic queries etc. You can also still issue native SQL, and also queries by “Criteria”

(specified using “parse tree” of Java objects) Hibernate Mapping - Uses HBM XML files to map value objects (POJOs) to

database tables Transparent persistence - Allows easy saves/delete/retrieve for simple

value objects Very high performance “in general” due to intelligent (2-level) caching,

although in a few cases hand-written SQL might beat it

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Hibernate Hibernate basically sits between the DB and

your code Can map persistent objects to tables

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Database Design

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7.4 Database Design Purpose Overview Steps Map persistent design classes to tables Distribute class behavior to the database

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Purpose To ensure that persistent data is stored consistently

and efficiently. To define behavior that must be implemented in the

database.

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Database Design Overview

SupplementarySpecifications

DatabaseDesign

Use-Case Realization

Design Classes

DesignGuidelines

Data Model

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Steps Map Persistent Design Classes to the Data Model Optimize the Data Model for Performance Optimize Data Access Define Storage Characteristics Define Reference Tables Define Data and Referential Integrity Enforcement Rules Distribute Class Behavior to the Database Review the Results

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Mapping Persistent Classes to Tables In a relational database

Every row is regarded as an object A column in a table is equivalent to a persistent

attribute of a class

Student

- name : String- address : String- studentID : Long

Name Student_ID

Thomas Stuart 123456

Object Instance

Attributes from object type

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Mapping Persistent Classes to Tables - Example

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Map Class Behavior to Stored Procedures Determine if any operations can be

implemented as a stored procedure Candidate operations

Deal with persistent data Any operations where a query is involved in a

computation Need to access the database to validate data

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What Are Stored Procedures? A stored procedure is executable code

which runs under the RDBMS Two types of stored procedures

Procedures: Executed explicitly by an application

Triggers: Invoked implicitly when some database event occurs

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Example: Map Class Behavior to Stored Procedures

Student.

+ getTuition()+ addSchedule()+ getSchedule()+ deleteSchedule()+ hasPrerequisites()# passed()<<class>> + getNextAvailID()+ getStudentID()+ getName()+ getAddress()

Class Candidate Operations• getTuition

• addSchedule

• getSchedule

• deleteSchedule

• getStudentID

• getName

• getAddress

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Example: Map Class Behavior to Stored Procedures