data 1

Problems with File System Data Processing

1Even simple file system retrieval task required extensive programming Ad hoc queries impossible Changing existing structure difficult 2Security features difficult to program Often omitted in file system environments 3Summary of file system limitations: Requires extensive programming Cannot perform ad hoc queries System administration is complex and difficult Difficult to make changes to existing structures Security features are likely to be inadequate

Evolution of File System Data Processing

1File systems typically composed of collection of file folders, each tagged and kept in cabinet Organized by expected use Contents of each file folder are logically related 2Manual file systems Served as a data repository for small data collections Cumbersome for large collections 3Computerized file systems Data processing (DP) specialist converted computer file structure from manual system Wrote software that managed the data Designed the application programs Initially, computer file systems resembled manual systems As number of files increased, file systems evolved Each file used its own application program to store, retrieve, and modify data Each file was owned by individual or department that commissioned its creation

Summary

Data are raw facts Information is the result of processing data to reveal its meaning Accurate, relevant, and timely information is the key to good decision making DBMS implements a database and manages its contents Metadata is data about data Database design defines the database structure Well-designed database facilitates data management and generates valuable information Poorly designed database leads to bad decision making and organizational failure

Data vs. Information

Data are raw facts Information is the result of processing raw data to reveal meaning Information requires context to reveal meaning Raw data must be formatted for storage, processing, and presentation Data are the foundation of information, which is the bedrock of knowledge

Data Redundancy (cont'd.)

Data inconsistency: different and conflicting versions of same data occur at different places Data anomalies: abnormalities when all changes in redundant data are not made correctly Update anomalies Insertion anomalies Deletion anomalies

DBMS Functions (cont'd.)

Data integrity management DBMS promotes and enforces integrity rules Minimizes redundancy Maximizes consistency Data relationships stored in data dictionary used to enforce data integrity Integrity is especially important in transaction-oriented database systems

DBMS Functions (cont'd.)

Data storage management DBMS creates and manages complex structures required for data storage Also stores related data entry forms, screen definitions, report definitions, etc. Performance tuning: activities that make the database perform more efficiently DBMS stores the database in multiple physical data files

DBMS Functions (cont'd.)

Data transformation and presentation DBMS transforms data entered to conform to required data structures DBMS transforms physically retrieved data to conform to user's logical expectations Security management DBMS creates a security system that enforces user security and data privacy Security rules determine which users can access the database, which items can be accessed, etc.

Data vs. Information (cont'd.)

Data: building blocks of information Information produced by processing data Information used to reveal meaning in data Accurate, relevant, timely information is the key to good decision making Good decision making is the key to organizational survival

DBMS Functions (cont'd.)

Database access languages and application programming interfaces DBMS provides access through a query language Query language is a nonprocedural language Structured Query Language (SQL) is the de facto query language Standard supported by majority of DBMS vendors

DBMS Functions (cont'd.)

Database communication interfaces Current DBMSs accept end-user requests via multiple different network environments Communications accomplished in several ways: End users generate answers to queries by filling in screen forms through Web browser DBMS automatically publishes predefined reports on a Web site DBMS connects to third-party systems to distribute information via e-mail

Database Systems

Database system consists of logically related data stored in a single logical data repository May be physically distributed among multiple storage facilities DBMS eliminates most of file system's problems Current generation stores data structures, relationships between structures, and access paths Also defines, stores, and manages all access paths and components

The Database System Environment

Database system: defines and regulates the collection, storage, management, use of data Five major parts of a database system: Hardware Software People Procedures Data

Managing the Database System: A Shift in Focus

Disadvantages of database systems: Increased costs Management complexity Maintaining currency Vendor dependence Frequent upgrade/replacement cycles

Data Redundancy

File system structure makes it difficult to combine data from multiple sources Vulnerable to security breaches Organizational structure promotes storage of same data in different locations Islands of information Data stored in different locations is unlikely to be updated consistently Data redundancy: same data stored unnecessarily in different places

The Database System Environment

Hardware: all the system's physical devices Software: three types of software required Operating system software DBMS software Application programs and utility software

Summary (cont'd.)

In a file system, data stored in independent files, each requires its own management program Some limitations of file system data management: Requires extensive programming System administration is complex and difficult Changing existing structures is difficult Security features are likely inadequate Independent files tend to contain redundant data Database management systems were developed to address file system's inherent weaknesses DBMS present database to end user as single repository Promotes data sharing Eliminates islands of information DBMS enforces data integrity, eliminates redundancy, and promotes security

DBMS Functions

Most functions are transparent to end users Can only be achieved through the DBMS Data dictionary management DBMS stores definitions of data elements and relationships (metadata) in a data dictionary DBMS looks up required data component structures and relationships Changes automatically recorded in the dictionary DBMS provides data abstraction and removes structural and data dependency

DBMS Functions (cont'd.)

Multiuser access control DBMS uses sophisticated algorithms to ensure concurrent access does not affect integrity Backup and recovery management DBMS provides backup and data recovery to ensure data safety and integrity Recovery management deals with recovery of database after a failure Critical to preserving database's integrity

The Database System Environment (cont'd.)

People: all users of the database system System and database administrators Database designers Systems analysts and programmers End users Procedures: instructions and rules that govern the design and use of the database system Data: the collection of facts stored in the database

Structural and Data Dependence (cont'd.)

Practical significance of data dependence is difference between logical and physical format Logical data format: how human views the data Physical data format: how computer must work with data Each program must contain: Lines specifying opening of specific file type Record specification Field definitions

Database: shared, integrated computer structure that stores a collection of: End-user data: raw facts of interest to end user Metadata: data about data Provides description of data characteristics and relationships in data Complements and expands value of data Database management system (DBMS): collection of programs Manages structure and controls access to data

Role and Advantages of the DBMS: DBMS is the intermediary between the user and the database Database structure stored as file collection Can only access files through the DBMS DBMS enables data to be shared DBMS integrates many users' views of the data

Structural and Data Dependence

Structural dependence: access to a file is dependent on its own structure All file system programs must be modified to conform to a new file structure Structural independence: change file structure without affecting data access Data dependence: data access changes when data storage characteristics change Data independence: data storage characteristics do not affect data access

File System Redux: Modern End-User Productivity Tools

Ubiquitous use of personal productivity tools can introduce the same problems as the old file systems Microsoft Excel Widely used by business users Users have become so adept at working with spreadsheets, they tend to use them to complete tasks for which spreadsheets are not appropriate - database substitute

Advantages of a DBMS: Improved data sharing Improved data security Better data integration Minimized data inconsistency Improved data access Improved decision making Increased end-user productivity

Why Database Design Is Important: ~Database design focuses on design of database structure used for end-user data Designer must identify database's expected use 1Well-designed database: Facilitates data management Generates accurate and valuable information 2Poorly designed database: Causes difficult-to-trace errors