Database and Legacy Systems

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Transcript Database and Legacy Systems

ASPECTS OF FILE PROCESSING APPROACH

USERS HAVE REQUIREMENTS FOR INFORMATION SYSTEM
APPLICATIONS.

USERS EITHER “COMMISSION” IS STAFF TO DEVELOP
APPLICATION, OUTSOURCE IT, OR INCREASINGLY, DEVELOP
IT THEMSELVES USING PC SOFTWARE.

REGARDLESS OF WHO DOES IT, PROGRAMMING PROCESS IS
ERROR-PRONE AND TIME-CONSUMING.

EACH APPLICATION REQUIRES ITS OWN DATA IN ITS OWN
FORMATS STORED IN ITS OWN FILES.
Orders Department
Program
A
Program
B
Accounting Department
Program
C
Order Filling
System
Customer
Master
file
Inventory
Master
file
Program
A
Program
B
Invoicing
System
Back
Order
file
Inventory
Pricing
file
Customer
Master
file
Payroll Department
Program
A
Program
C
Payroll
System
Employee
Master
file
PROBLEMS WITH
FILE PROCESSING ENVIRONMENT

UNCONTROLLED REDUNDANCY
- Data
- Programs

DATA INCONSISTENCY
- Redundant data is difficult to keep “in synch”

LIMITED SHARING OF DATA
- File structure incompatibility (ex: ISAM vs Direct Access)
- System software incompatibility (ex: Oracle vs M/S Access)

INFLEXIBILITY OF AVAILABLE INFORMATION
- Files tend to isolate information and restrict what can be retrieved

POOR ENFORCEMENT OF STANDARDS
- “Random” naming conventions (ex: homonyms and synonyms)

INFORMATION RESOURCE MANAGEMENT MORE DIFFICULT
- Program maintenance
(exs: “Which systems use which data?”
“If we convert from 5-digit to 9-digit zip codes, what programs
need to be changed?”;
“What files and programs are not Y2K compatible?”)
- Data security: multiple files ==> more vulnerability
ELEMENTS OF DB APPROACH
(1) DATA AS A RESOURCE
Data considered as a resource in same
way hardware/software/personnel are
considered as resources.
(2) DATA INDEPENDENCE
Data format/structure independent of
particular application.
User view of data not tied to physical
representation of data.
(3) DATABASE MANAGEMENT SYSTEM (DBMS)
DBMS is software which coordinates data
resources in the same way that an operating
system (OS) coordinates system resources.
(4) DATABASE MANAGEMENT
The management of hardware/software/
DBMS/data which implements DB approach.
DATABASE APPROACH
(1) Put data into common databases that
can be accessed and shared by multiple users.
Appl.
Prog. 1
DB1
DB2
DB3
Appl.
Prog. 2
Shared Data
Resource
(2) Provide uniform storage, access, and
retrieval methodology for data.
Ex: High level commands like STORE,
UPDATE, RETRIEVE, etc.
(3) Provide generalized, user-friendly
interfaces so non-DP personnel may
interact directly with data without
programmer’s aid.
Ex: Query language (SQL),
DB application generators
(PowerBuilder, M/S Access)
BENEFITS OF DATABASE PROCESSING

MINIMAL DATA REDUNDANCY
Redundancy reduced (not eliminated) ==> controlled redundancy.

CONSISTENCY OF DATA
Inconsistency managed via single, centralized source of data.

INTEGRATION OF DATA
Data are organized into single, logical structure with logical relationships
between “files”;
Files can be “joined”, or integrated, where it makes sense; files no longer in
isolation.

SHARING OF DATA
All programs access same data using standardized commands;
DBMS supports multiple file structures;
Separate “views” of a database can be created for each user.

DATA ACCESSIBILITY AND RESPONSIVENESS
DBMS supports programmed and unanticipated queries and reports via SQL;

UNIFORM SECURITY, PRIVACY, AND INTEGRITY CONTROLS
Centralized data facilitates standards and controls;
DBMS provides data integrity features (ex: security, concurrency, transaction
recovery, etc.).

SUPPORTS IRM AND REDUCED PROGRAM MAINTENANCE
Dictionary, or repository, stores data about information resources;

APPLICATION AND DATA INDEPENDENCE
Data can be changed without changing application programs

EASE OF APPLICATION DEVELOPMENT
Database application environments (e.g., PowerBuilder for Oracle)
CHALLENGES OF DATABASE APPROACH

ORGANIZATIONAL CONFLICT
Data ownership (“Information is power.”);
Implementation of data standards.

SPECIALIZED PERSONNEL
Database personnel (database analysts, DBA, etc) require special skills and
training.

EXTENSIVE OVERHEAD OF MAINTAINING DATA INTEGRITY
Security, privacy, concurrency, recovery and backups.

DISTRIBUTED DATA MANAGEMENT
Data management is centralized in its approach whereas distributed
computing over networks is decentralized.
•
MAKING DATA AVAILABLE ON THE WEB
Data warehouses are used to store large amounts of time-series data for
management analysis and decision-making.
COMPONENTS OF A DATABASE SYSTEM

DATABASE
- User Data
- Metadata
- Indexes
- Application Metadata
•
DATABASE MANAGEMENT SYSTEM (DBMS)
- Design tools subsystem
- Run-Time subsystem
- DBMS Engine
Data integrity
Data dictionary

APPLICATIONS
- Forms
- Queries
- Reports
- Menus
- Application Programs
KINDS OF DATA IN A DATABASE

RECORD-BASED SOURCE DATA
BITS => BYTES => FIELDS => RECORDS => FILES => DB

META-DATA
DATA ABOUT DATA IN THE DATABASE. (E.g., information about the
data fields, their data types, and acceptable data values, etc.)
DATA ABOUT APPLICATIONS (E.g., forms, queries, reports, etc.)

OVERHEAD DATA
INDEXES, KEYS, ETC.

OTHER SOURCE DATA (Bit Map Data)
VOICE
IMAGES
ANIMATION
VIDEO
FUNCTIONS OF A DBMS

DATA DEFINITION

Define and store database structure called the Schema
(Metadata + Overhead Data)

Load source data into database

Provide multiple views of data

DATA MANIPULATION

Provide variety of access methods to tables
(ISAM, direct, B-tree, sequential, etc.)

Query processing (SQL)

Provide database interface commands in existing programming
languages such as C++, Java, C, Cobol.

DATA INTEGRITY AND CONTROL

Security

Concurrent processing

Backup and recovery

Referential integrity

APPLICATION ENVIRONMENT

Programming language (e.g., VisualBasic)

Menus, screens, forms and reports
APPLICATION ENVIRONMENTS FOR DB
PROCESSING

LOOSELY-COUPLED vs TIGHTLY-COUPLED
Access Basic vs Visual Basic or C++

DESIGN TOOLS
Table creation tool
Form creation tool
Query creation tool
Report creation tool
Procedural language compiler

RUN-TIME TOOLS
Form processor
Query processor
Report writer
Procedural language run-time