Chap 11 Old

8/7/2019 Chap 11 Old

1/84

Ob ect-Oriented S stems Develo ment Bahrami Irwin/ McGraw-Hill

Chapter 11:

Access Layer: Object Storage

and Object Interoperability

ObjectObject--Oriented SystemsOriented SystemsDevelopmentDevelopment:Using the Unified ModelingUsing the Unified Modeling

LanguageLanguage

8/7/2019 Chap 11 Old

2/84


Goals

Object storage and persistence.

Database management systems andtheir technology.

Client-server computing.

Distributed databases.Distributed object computing.

8/7/2019 Chap 11 Old

3/84


Goals (Cont)

Object-oriented database

management systems.Object-relational systems.

Designing access layer objects.

8/7/2019 Chap 11 Old

4/84


Introduction

A database management system(DBMS) is a collection of relateddata and associated programs thataccess, manipulate, protect andmanage data.

8/7/2019 Chap 11 Old

5/84


Whats the purpose of DBMSThe main purpose of a DBMS is to

provide a reliable, persistent data

storage facility,and mechanism for efficient

and convenient data access and

retrieval.

8/7/2019 Chap 11 Old

6/84


Persistence (review)Persistence is defined as objects

that outlive the programs whichcreated them.

Persistent object stores do notsupport query or interactive userinterface facilities, as found in afully supported DBMS orOODBMS.

8/7/2019 Chap 11 Old

7/84


Object Storage andPersistenceAtkinson et al. describe six broad

categories for the lifetime of data:

1. Transient results to the evaluation

of expressions. 2. Variables involved in procedure

activation (parameters and variables

with a localized scope). 3. Global variables and variables

that are dynamically allocated.

8/7/2019 Chap 11 Old

8/84


Object Storage andPersistence(Cont)

4. Data that exist between the

executions of a program. 5. Data that exist between the

versions of a program.

6. Data that outlive a program.

8/7/2019 Chap 11 Old

9/84


Database Management Systems

A DBMS is a set of programs thatenable the creation and maintenance

of a collection of related data. DBMS have a number of properties

that distinguish them from the file-

based data management approach.

8/7/2019 Chap 11 Old

10/84


Database system Vs. File System.

Engineering

Accounting

Marketing

Accounting

Sal

u t

Em l

I v t r

u t m r Part

Database

DBMS

Marketing

Engineering Parts

Customer

Sales

Inventory

Accounts

File System

A Database System

8/7/2019 Chap 11 Old

11/84


Database Models A database model is a collection of

logical constructs used to represent the

data structure and data relationshipswithin the database.

Hierarchical Model

Network Model

Relational Model

8/7/2019 Chap 11 Old

12/84


H

ierarchical model

Motor Vehicle

Truck CarBus

The hierarchical model representsdata as a single-rooted tree.

8/7/2019 Chap 11 Old

13/84


Network model

Cust r up

Ord r

A network database model is similarto a hierarchical database, with onedistinction.

Unlike the hierarchical model, anetwork model's record can have more

than one parent.

8/7/2019 Chap 11 Old

14/84


Relational Model

Of all the database models, therelational model has the simplest,

most uniform structure and is themost commercially widespread.

8/7/2019 Chap 11 Old

15/84


Relational Database (Cont)

Soup NSoup-I ric

So p Table

NCust-I ddr ss hone #

C sto er Table

Cust-ISoup-I QTY

Order Table

Order-IKey

KeyKey

Foreign

Keys

8/7/2019 Chap 11 Old

16/84


What is a schema andmetadata? The schema, or metadata, contains a

complete definition of the dataformats, such as the data structures,

types, and constraints.

8/7/2019 Chap 11 Old

17/84


Schema (Cont) In an object-oriented DBMS, the

schema is the collection of class

definitions.The relationships among classes

(such as super/sub) are

maintained as part of the schema.

8/7/2019 Chap 11 Old

18/84


Database Definition Language

(DDL)A database definition language

(DDL) is used to describe thestructure of and relationshipsbetween objects stored in adatabase.

8/7/2019 Chap 11 Old

19/84


Data Manipulation Language

(DML)Once data is stored in a database,

there must be a way to get it, use it,and manipulate it.

DML is a language that allows users

to access and manipulate (such as:creation, saving and destruction of)data organization.

8/7/2019 Chap 11 Old

20/84


DML (Cont)The Structured Query Language

(SQL) is the standard DML forrelational DBMS.

In a relational DBMS, the DML isindependent from a hostprogramming language.

8/7/2019 Chap 11 Old

21/84


DML (Cont)For example, a host language such as

C or COBOL would be used to writethe body of the application.

SQL statements are then typically

embedded in C or COBOLapplications to manipulate data.

8/7/2019 Chap 11 Old

22/84


ShareabilityData in the database often needs

to be accessed and shared bydifferent applications.

The database then must detect andmediate the conflicts and promotethe greatest amount of sharing

possible withoutsacrificing theintegrity of data.

8/7/2019 Chap 11 Old

23/84


TransactionAtransaction is a unit of change, in

which either all changes to objectswithin a transaction will be applied

or not at all.A transaction is said to commitif all

changes can be successfully made to

the database and to abortif allchanges cannot be successfullymade to the database.

8/7/2019 Chap 11 Old

24/84


Concurrency Control

Programs will attempt to read andwrite the same pieces of information

simultaneously and, in doing so,create a contention for data.

The concurrency

control mechanism isthus established to

mediate these conflicts.

8/7/2019 Chap 11 Old

25/84


Concurrency Control (Cont) It does so by making policies that

dictate how read and write conflictswill be handled.

8/7/2019 Chap 11 Old

26/84


Concurrency Control (Cont)The most conservative way is to

allow a user to lock all records or

objects when they are accessedand to release the locks only aftera transaction commits.

8/7/2019 Chap 11 Old

27/84


Concurrency Control (Cont)

By distinguishing betweenreading the data, and writing it(which is achieved by qualifying thetype of lock placed in the data-readlock or write lock) somewhat greaterconcurrency can be achieved.

This policy allows manyreaders of a record or anobjective, but only one writer.

8/7/2019 Chap 11 Old

28/84


Distributed Databases In distributed databases portions of

the database reside on differentnodes (computers) in the network.

8/7/2019 Chap 11 Old

29/84


Client/Server ComputingClient/server computing allows

objects to be executed in different

memory spaces or even differentmachines.

8/7/2019 Chap 11 Old

30/84


Client/Server Computing (Cont)

The calling module becomes the"client" (which requests a service),and the called module becomesthe "server" (which provides theservice).

8/7/2019 Chap 11 Old

31/84


Client/Server Computing (Cont)Client programs usually manage:

The user-interface

Validate data entered by the user

Dispatch requests to server

programs, and sometimesExecute business logic.

8/7/2019 Chap 11 Old

32/84


Client/Server Computing (Cont)The Business layer contains all of

the objects that represent thebusiness such as:

Order

Customer Line Item

Inventory, etc.

8/7/2019 Chap 11 Old

33/84


Client/Server Computing (Cont)A server process (program) fulfills

the client request by performingthe task requested.

Server programs generally receiverequests from client programs,execute database retrieval andupdates, manage dataintegrity, and dispatchresponses to client requests.

8/7/2019 Chap 11 Old

34/84


Atwo-tierarchitecture is onewhere a client talks directly to aserver, with no intervening server.

This type of architecture istypically used in smallenvironments with lessthan 50 users.

ATwo-TierArchitecture

8/7/2019 Chap 11 Old

35/84


ATwo-TierArchitecture (Cont)

SERVER

APPLICATION

CLIENTCLIENTCLIENT

LAN WAN

APPL. APPL. APPL.

Printer

Data

8/7/2019 Chap 11 Old

36/84


AThree-TierArchitectureA three-tier architecture

introduces another server (or an"agent") between the client and

the server.

The role of the agent is many fold.

I

t can provide translation servicesas in adapting a legacy applicationon a mainframe to a client/serverenvironment.

8/7/2019 Chap 11 Old

37/84


AThree-TierArchitecture (Cont)

UN X SERVER

Host (i.e. IBM 3090)

CLIENT

Sy ase RDBMS

Legacy a lications: DB2 RDBMS

APPLICATION SWindo s 9x

ACCES S

Lotus

Agent

8/7/2019 Chap 11 Old

38/84


Basic Characteristics of

Client/ServerArchitectures1. The client or front-end interacts

with the user, and a server or back-end interacts with the sharedresource.

8/7/2019 Chap 11 Old

39/84



Client/ServerArchitectures (Cont)2. The front-end task and back-end

task have fundamentally differentrequirements for computingresources.

Resources such as processor speeds,memory, disk speeds and capacities,and input/output devices.

8/7/2019 Chap 11 Old

40/84


3. The environment is typicallyheterogeneous and multi-vendor.


Client/ServerArchitectures (Cont)

8/7/2019 Chap 11 Old

41/84



Client/ServerArchitectures (Cont)4. Client-server systems can be

scaled horizontally or vertically.

Horizontal scaling means adding orremoving client workstations withonly a slight performance impact.

Vertical scaling means migrating toa larger and faster server machine ormulti servers.

8/7/2019 Chap 11 Old

42/84


DistributedProcessingDistributed processing implies that

processing will occur on more thanone processor in order for a

transaction to be completed.

S e r v e r S e r v e r 1

C l i e n t C l i e n t C l i e n t

l i c t i n

F r e n t 1

l i c t i n

F r e n t

8/7/2019 Chap 11 Old

43/84


DistributedProcessing (Cont)

For example, in processing an orderfrom our client, the client

information may process at onemachine and the accountinformation will then be processed

next on a different machine.

8/7/2019 Chap 11 Old

44/84


Cooperative processing

Cooperative processing is a form ofdistributed computing where two ormore distinct processes are required

to complete a single businesstransaction.

C o o e ra t i e P r o c e s s in g

A P P L I C A T I O N SW in d o s 9 x

A C C E S S

L otu s

A P P L I C A T I O N S

W in do s 9 xA C C E S S

L otu s

S E R V E R

8/7/2019 Chap 11 Old

45/84


Client/Server Components

I. User Interface Layer: This is one ofthe major components of theclient/server application.

It interacts with users, screens,

Windows, Window management,keyboard, and mouse handling.

8/7/2019 Chap 11 Old

46/84


Client/Server Components (Cont)

II. Business Processing Layer: This isa part of the application that usesthe user interface data to performbusiness tasks.

8/7/2019 Chap 11 Old

47/84


Client/Server Components (Cont)

III. Database Processing Layer: Thisis a part of the application code

that manipulates data within theapplication.

8/7/2019 Chap 11 Old

48/84


Distributed Object Computing (DOC)

Distributed object computingpromises the most flexible

client/server systems. It utilizes reusable software

components that can roam anywhere

on networks, run on differentplatforms, communicate with legacyapplications.

8/7/2019 Chap 11 Old

49/84


DOC (Cont)

Currently, there are severalcompeting DOC standards,including:

Microsoft's ActiveX/DCOM

the Object Management Group'sCORBA, and

OpenDoc.

8/7/2019 Chap 11 Old

50/84


Common ObjectRequest Broker

Architecture (CORBA)CORBA provides means to

integrate distributed, heterogeneous

business applications and data.The CORBAInterface Definition

Language (IDL) allows developers to

specify language-neutral, object-oriented interfaces for applicationand system components.

8/7/2019 Chap 11 Old

51/84


ObjectRequest Brokers (ORBs)

ORBs implement a communicationchannel through which applications canaccess object interfaces and request data

and services.

Object Request roker (OR )

DomainObjects

NamingPersistenc

eE ents

oncurrency

Transaction

ApplicationObjects

8/7/2019 Chap 11 Old

52/84


Microsoft's ActiveX/DCOM

The Distributed Component Objectmodel, Microsoft's alternative toOMG's CORBA.

DCOM is an Internet andcomponent strategy where ActiveX(formerly known as object linkingand embedding, or OLE) plays therole of DCOM object.

8/7/2019 Chap 11 Old

53/84


Object-Oriented Database Systems

Database

apabilities

DataE

apsulati

P

l

mrphis

m

bject-

rientedpr

ramming

Object

Identit

Object&

lass

Concurrenc

y

Security

Recover

y

Quer

y

Integrity

Versioning

Archiv

e

Persistenc

e

Inheritanc

e

The object-orienteddatabase management

system is a marriageof object-orientedprogramming anddatabase technology

to provide what wenow call object-oriented databases.

8/7/2019 Chap 11 Old

54/84


Object-Oriented Database System

ManifestoMalcolm Atkinson et al. described

the necessary characteristics that a

system must satisfy to be consideredan object-oriented database.

These categories can be broadly

divided into object-orientedlanguage properties anddatabase requirements.

8/7/2019 Chap 11 Old

55/84


Manifesto (Cont)First, the rules that make it an object-oriented system are as follows:

1. The system must support complex objects.

2. Object identity must be supported.

3. Objects must be encapsulated.

4. The system must support types or classes.

5. The system must support inheritance.

6. The system must avoid prematurebinding.

7. The system must be computationally

complete.

8/7/2019 Chap 11 Old

56/84


Manifesto (Cont) 8. The system must be extensible.

Second, these rules make it a DBMS:

9. It must be persistent, able to remember an

object state. 10. It must be able to manage very large

databases.

11. It must accept concurrent users.

12. It must be able to recover from hardwareand software failures.

13. Data query must be simple.

8/7/2019 Chap 11 Old

57/84


Object-Oriented Databases versus

Traditional DatabasesThe objects are an "active"

component in an object-orienteddatabase.

Relational database systems do notexplicitly provide inheritance ofattributes and methods.

8/7/2019 Chap 11 Old

58/84


Object-Oriented Databases versus

Traditional Databases (Cont)Each object has its own identity, or

object-ID (as opposed to the purelyvalue-oriented approach oftraditional databases).

Object identity allows objects to berelated as well as shared within adistributed computing network.

8/7/2019 Chap 11 Old

59/84


Object-Relational Systems: The

Practical World In practice, even though many

applications increasingly aredeveloped in an object-orientedenvironment, chances are good thatthe data those applications need to

access live in a very differentuniversea relational database.

8/7/2019 Chap 11 Old

60/84


Object-Relation Mapping

For a tool to be able to define howrelational data maps to and fromapplication objects, it must have at least

the following mapping capabilities: Table-class mapping.

Table-multiple classes mapping.

Table-inherited classes mapping.

Tables-inherited classes mapping.

8/7/2019 Chap 11 Old

61/84


Table-Class Mapping

Each row in the table represents an objectinstance and each column in the tablecorresponds to an object attribute.

Car

cost

color

ke

model

cost color make model

Car Table

8/7/2019 Chap 11 Old

62/84


Table-Multiple Classes Mapping

The custID column provides the discriminant.If the value for custID is null, an Employeeinstance is created at run time; otherwise, aC stomerinstance is created. Employee

name

address

empIname custIaddress

Person Table

empI

C stomer

name

address

custI

8/7/2019 Chap 11 Old

63/84


Table-Inherited Classes Mapping

Employee

name

ssn

name address

Person Table

ssn

Ho rlyEmployee

wage

SalariedEmployee

address

salar

wage salar

Instances of SalariedEmployee can be created for anyrow in the Person table that has a non null value forthe salary column. If salary is null, the row isrepresented by an Ho rlyEmployee instance.

8/7/2019 Chap 11 Old

64/84


Tables-Inherited Classes Mapping

name

name address

Person Table

dept

C

stomer

address

company

Employee

Person

name

Employee Table

ssn

name address

C stomer Table

ssn

ssn

dept

company

salary

salary

Instances ofP

erson aremapped directly from

the Person table.

Howe er, instances of

Employee can be

created only for the

rows in the Employeetable (the joins of the

Employee and Person

tables on the ssn key).

The ssn is sed both

as a prim

ary key on thePerson table and as a

foreign key on the

Person table and a

primary key on the

Employee table for

acti ating instances of

8/7/2019 Chap 11 Old

65/84


Keys forInstanceNavigation

name

Department able

Department

name

Employee

name

Employee able

ssnpartment ID salary

salary

epartment ID

name

ssn

epartment ID

The departmentID

property of Employee

uses the foreign key in

column

Employee.departmentID

.Each Employee instance

has a direct reference of

class Department

(association) to the

department object to

which it belongs.

8/7/2019 Chap 11 Old

66/84


Multidatabase System

A different approach for integratingobject-oriented applications withrelational data environments is

multidatabase systems, orheterogeneous database systems,which facilitate the integration of

heterogeneous databases and otherinformation sources.

8/7/2019 Chap 11 Old

67/84


Federated Multidatabase SystemsFederated multidatabase systems

provide a solution to the problem ofinteroperating heterogeneous data

systems, provide uniform access todata stored in multiple databasesthat involve several different data

models.

8/7/2019 Chap 11 Old

68/84

8/7/2019 Chap 11 Old

69/84


Characteristics of MDBSAutomatic generation of a unifiedglobal database schema from localdatabases.

Provision of cross-databasefunctionality (global queries, updates,and transactions) by using unified

schemata. Integration of a heterogeneous database

system with multiple databases.

8/7/2019 Chap 11 Old

70/84


Characteristics of MDBS (Cont)

Integration of data types other thanrelational data through the use of

such tools as driver generators.Provision of a uniform but diverse

set of interfaces (e.g., a SQL-style

interface, browsing tools, and C++)to access and manipulate data storedin local databases.

8/7/2019 Chap 11 Old

71/84


Open Database Connectivity

Open database connectivity(ODBC), provides a mechanism forcreating a virtual DBMS.

Applicationprograms

ODBCdriver manager

Database A

Database B

Database C

Database D

Database E

oadableODBCdriver

Driver fordatabaseA

Driver fordatabaseB

Driver fordatabaseC

Driver forDatabaseD

Driver fordatabase E

...

ODBC

API

8/7/2019 Chap 11 Old

72/84


DesigningAccess Layer Classes

The main idea behind creating an accesslayer is to create a set of classes thatknow how to communicate with data

source, whether it be a file, relationaldatabase, mainframe, Internet, DCOM,or via ORB.

The access classes must be able totranslate any data-related requests from

the business layer into the appropriate

protocol for data access.

8/7/2019 Chap 11 Old

73/84


Access Layer Classes (Cont)

The business layerobjects and iew

layer objects should

not directly access

the database.Instead, they

should consult with

the access layer for

all external system

connecti ity.

Database, ORB, Internet, etc.

View layer objects

Business Layer Objects

Access Layer Objects

Application /

Ser er

ClientClientClient

DBMS Seor

Legacy dat

applicatio

8/7/2019 Chap 11 Old

74/84


Benefits ofAccess Layer ClassesA

ccess layer classes provide easymigration to emerging distributedobject technology, such as CORBA andDCOM.

These classes should be able toaddress the (relatively) modest needs

of two-tier client/server architecturesas well as the difficult demands offine-grained, peer-to-peer distributed

object architectures.

8/7/2019 Chap 11 Old

75/84


Process

The access layer design process consistsof these following activities:

1.If methods will be stored in a program then

For every business class identified, determine if the

class has persistent data.

else

For every business class identified, mirror the

business class package.

2.Define relationships. The same rule as applies among

business class objects also applies among access

classes.

8/7/2019 Chap 11 Old

76/84


Process (Cont)

3.Simplify classes and relationships. The main goalhere is to eliminate redundant or unnecessary classes

or structures.

3.1.Redundant classes. If you have more than one

class that provides similar services, simply select

one and eliminate the other(s).

3.2.Method classes. Revisit the classes that consist

of only one or two methods to see if they can beeliminated or combined with existing classes.

4. Iterate and refine.

8/7/2019 Chap 11 Old

77/84


Process of CreatingAccess Layer

ClassesBusiness

Layer

Access

Layer

Class1

Class2 Class3

Step1: irrorbusinessclasspackage

Class1DB

Class2DB Class3DB

Access

layer

Class1DB

Class2DB Class3DB

Step2:Define relationships

Access

layer

Access

layer

Class1

Class2 Class3

Class1DB

Class2DB Class3DB

Step3: Simplifyclassesand relationships

8/7/2019 Chap 11 Old

78/84


Access Layer Classes (Cont)

The relationbetween a

business class andits associatedaccess class.

Class1

Class1DB

Business class

Access classfor Class1

8/7/2019 Chap 11 Old

79/84


SummaryT

he fundamental purpose of aDBMS is to provide a reliablepersistent data storage facility and

the mechanisms for efficient,convenient data access and retrieval.

Many modern databases are

distributed databases.

8/7/2019 Chap 11 Old

80/84


Summary (Cont)Client/server computing is the logical

extension of modular programming.

Distributed computing is a second

client/server revolution, a transitionto an immensely expandedclient/server era.

The object-oriented databasetechnology is a marriage of object-

oriented programming and database

technology.

8/7/2019 Chap 11 Old

81/84


Summary (Cont)

In practice, e en though manyapplications increasingly are de eloped

using object-oriented programming

technology, the data those applicationsneed to access li e in a relational

database.

8/7/2019 Chap 11 Old

82/84


Summary (Cont)

The main process in relational-object

integration is defining the relationships

between the table structures

(represented as schemata) in the

relational database with classes

(representing classes) in the object

model.

8/7/2019 Chap 11 Old

83/84


Summary (Cont)

A different approach for integratingobject-oriented applications with

relational data environmentsinvolves multidatabase systems, orheterogeneous database systems,

which facilitate the integration ofheterogeneous databases and otherinformation sources.

8/7/2019 Chap 11 Old

84/84

Chap 11 Old

Documents

Transcript of Chap 11 Old