Database and Legacy Systems
Database and Legacy Systems
ASPECTS OF FILE PROCESSING APPROACH
USERS HAVE REQUIREMENTS FOR INFORMATION SYSTEM
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.
FILE PROCESSING ENVIRONMENT
- 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
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.
(1) Put data into common databases that
can be accessed and shared by multiple users.
(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
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
Files can be “joined”, or integrated, where it makes sense; files no longer in
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
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
Data ownership (“Information is power.”);
Implementation of data standards.
Database personnel (database analysts, DBA, etc) require special skills and
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
- User Data
- Application Metadata
DATABASE MANAGEMENT SYSTEM (DBMS)
- Design tools subsystem
- Run-Time subsystem
- DBMS Engine
- Application Programs
KINDS OF DATA IN A DATABASE
RECORD-BASED SOURCE DATA
BITS => BYTES => FIELDS => RECORDS => FILES => DB
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.)
INDEXES, KEYS, ETC.
OTHER SOURCE DATA (Bit Map Data)
FUNCTIONS OF A DBMS
Define and store database structure called the Schema
(Metadata + Overhead Data)
Load source data into database
Provide multiple views of data
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
Backup and recovery
Programming language (e.g., VisualBasic)
Menus, screens, forms and reports
APPLICATION ENVIRONMENTS FOR DB
LOOSELY-COUPLED vs TIGHTLY-COUPLED
Access Basic vs Visual Basic or C++
Table creation tool
Form creation tool
Query creation tool
Report creation tool
Procedural language compiler
Procedural language run-time