## Database Systems:
###Design, Implementation, and Management

####Chapter 1: Database Systems

* objectives
- The difference between data and information
- What a database is
- Various types of databases
- Why they are valuable assets for decision making
- Importance of database design
- How modern databases evolved from file systems
- Flaws in file system data management
- Main components of database system
- Main functions of database management system (DBMS)

* Introduction
- Good decisions require good information derived from raw facts
- Data managed most efficiently when stored in a database
- Databases evolved from computer file systems

* Data Versus Information
- Data are raw facts
- Information is the result of processing 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 knowlegde
- 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 in the key to organizational survival

* The Database and the DBMS
- Database: shared, integrated computer structure that stores a collection of data
   -- End-user data: raw facts of intereset to the end user
   -- Metadata: data about data
- Metadata provides description of data charactertistics and relationships in data
   - Complements and expands the value of data
- Database management systems (DBMS): collection of programs that manage structure
   control 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
- Access database through the DBMS
- DBMS enables data to be shared
- DBMS integrates many user's views of the data
- Advantages of a DBMS:
   - Improved data sharing
   - Improved data security
   - Better data integration
   - Minimized data inconsistency
   - Improved decision making
   - Increased end-user productivity

* Types of Databases
- Databases can be classified according to:
   - Number of users
   - Database locations
   - Expected type and extent of use
- Single-user database: 
   - Supports only one user at a time
   - Desktop database: single user, runs on PC
- Multiuser database
   - Suports multiple users
   - Workgroup database supports a small number
   - Enterprise data supports a large number
- Centralized database: data stored at a single site
- Distributed database: data distributed across several different sites
- Operational database: supports a companie's day-to-day operations
- Data Warehouse: Stores data used for tactical or strategic decisions
- Unstructured data exist in their original state
- Structured data result from formatting 
   - Structure applied based on the type of processing to be performed
- Semistructured data have been processed to some extent
- XML database supports semistructured XML data

* Why database design is important
- Database design focuses on design of database structure used for end-user data
   - Designers must identify database's expected use
- Well-designed database:
   - Facilitates data management
   - Generates accurate and valuable information
- Poorly designed database
   - Caused difficult-to-trace errors

* Historical Roots: Files and File Systems
- Reasons for studying file systems:
   - Complexity of database design easier to understand
   - Understanding file system problems helps to avoid problems with DBMS systems
   - Knowledge of file system useful for converting file systems to database system
- File systems typically composed of collection of folders, each tagged and kept in cabinet
- Contents of each file folder logically related
- Manual system served as a data repository for small data collections
   -- Cumbersome for large collections
- Data Processing (DP) Specialist converted computer file structure from manual system
   - Wrote software that managed the data
   - Designed the applications programs
- Initially, computer file systems resembled manual systems
- As number of files increased, file systems evolved
   - Each files used its own application program to store, retrieve, and modify data
   - Each file owned by individual or department that commissioned its creation

* Problems with File System Data Management
- An improvement over manual systems
   - File systems used for over 2 decades
   - Understanding the shortcomings of file systems aids in development of modern databases
   - Many problems not unique to file systems
- Even simple file system retrieval task required extensive programming
   - Ad hoc queries impossible
   - Changing existing structure difficult
- Security features difficult to program

* Structural and Data Dependence
- Stuctural dependence: access to a file depends on its own structure
   - All file system programs must be modified to conform the the new file structure
- Structural independence: change file structure without accecting data access
- Data dependence: data access changes when data storage characteristics change
- Data independence: data storage characteristics do not affect data storage
- Practical significance of data dependence is difference between logical and physical format
   - Logical data format: how humans view the data
   - Phyisical data format: how computer must work with the data
- Each program must contain:
   - Lines specifying opening of specific file type
   - Record specification
   - Field definitions

* Field Definitions and Naming COnventions
- Storing customer name as a single field is a liability
   - Better record definition breaks fields into component parts
- Selecting proper field names important, field names are descriptive
   - With proper naming conventions, file structure becomes self-documenting
   - Some software places restrictions on the length of field names
- Each record should have a unique identifier

* Data Redundancy
- File system structure makes it difficult to combine data from multiple sources
- Organizational structure promotes storage of same data in different locations
   - islands of information
- Data stored in different locations unlikely to be updated consistently 
- The result is data redundancy: same data store unnecessarily in different places
- 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

* Database Systems
- Database system consists of logically related data stored in a single logical data repository
   - May be physically distributed among multiple stored facilities
- DBMS eliminates most the file system's problems
- Current generation stores data structures, relationships between structures, access paths
   - Takes care of defining, storing, and managing all access paths and components

* The Database System Environment
- Database system: defines and regulates the collection, storage, management, and use of data
- Five major parts of a database system:
   - Hardware
      - All the systems physical devices 
   - Software, People, Procedures, Data
      - OS
      - DBMS 
      - Application programs and utility software
   - People
      - All users of the database software
      - System and Database admins
      - 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

* DBMS Functions
- Most functions transparent to end users
   -Can only be achieved through the DBMS
- Data dictionary management
   - DBMS stores definitions of data elements and relationships (metadata) in the data dictionary
   - DBMS looks up required data components structures and relationships
   - Changes are automatically recorded in the dictionary
   - DBMS provides data abstraction, removes structural and data dependency
- 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
- 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
- Multiuser access control
   - DBMS uses sophisticated algorithms to ensure consurrent 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
- Data integrity management
   - DBMS promotes and enforces integrity rules
      - Minimized redundancy
      - Maximizes consistency 
   - Data relationships stored in data dictionary used to enforce data integrity
   - Integrity especially important in transaction-oriented database systems
- 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 languae
      - Standard supported by majority of DBMS vendors
- Database communication interfaces
   - Current DBMSs accept end-use requests via multiple different network environments
   - Communication 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 3rd party system to distribute information via email

* Managing the Database System: A shift in focus
- Database system provides a framework in which strict procedures and standards are enforced
   - ROle of human changes from programming to managin organization's resources
- Database system enables more sophisticated use of the data
- Data stuctures created within the database and their relationships determine effectiveness
- Disadvantages of database systems:
   - Increased costs
   - Management complexity
   - Maintaining concurrency
   - Vendor dependence
   - Frequent upgrade/replacement cycles