data management i dbms relational systems. overview u introduction u dbms –components –types u...
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Overview Introduction DBMS
– components– types
Relational Model– characteristics– implementation
Physical Structure
File-based Systems
Collection of applications that performs services for end user- programs define and manage data
Limitations– Data dependence-structure defined in program– Incompatible file formats– Programs written to satisfy function
Database Definition
A database system is essentially a computerized record keeping system whose overall purpose is to maintain information and make it available on demand
Advantages of Database REDUCED REDUNDANCY - Controlling duplication INTEGRATION AND SHARING OF DATA - One set of data to
maintain MAINTAINING CONSISTENCY - Data propagation DATA ACCESS - Multiple access paths; High level language STANDARDIZATION - Enforcing local and global standards SECURITY - User access; Protection of Data DATA INDEPENDENCE - Data descriptors separate from
application program Increased integrity and concurrency control
Components of a Database System Data
– Note: Date uses data and information interchangably Hardware
– Processor, main memory, secondary storage and I/O devices– Individual PC to a network of computers
Software– DBMS– Application programs– Others software tools
Users– Application Programmers– End - Users– DBA’s
Procedures ??
Database Management SystemDBMS
Software Software Components
– Data Definition DDL source form object form
– Data manipulation DML planned request unplanned request
– Data administration DAL Data security and recovery
– Integrity and concurrency– Performance– Data dictionary
Data DictionaryCatalog Repository
Database of information about a database
– description of all database objects
– references to all users of the database
– references to all programs and transactions that access the database
Provides the description of the data to enable program-data independence
Database Models Hierarchical - IMS
– tree structure with predefined access paths
– child has one parent Network - CODASYL - IDMS
– multiple paths to same record Multi-dimensional Object-oriented
– data and methods
– highly-variable structure
– tightly coupled with programming language Hybrid - Object/Relational Databases
Relational Model
Evolving System - System designed by Codd, partially implemented, developing
Theoretical Vs Available - No system met Codd’s original 12 rules. Degrees of relational defined
Date’s work - Supportive of relational model but not always in agreement with Codd
Functions of a DBMS Data Storage, Retrieval and Update.
– Must furnish users with the ability to store, retrieve, and update data in the database.
A User-Accessible Catalog.– Must furnish a catalog in which descriptions of data
items are stored and which is accessible to users. Transaction Support
– Must furnish a mechanism to ensure that either all the updates corresponding to a given transaction are made or that none of them are made.
Functions of a DBMS Concurrency Control Services
– Must furnish a mechanism to ensure that database is updated correctly when multiple users are updating the database concurrently.
Recovery Services– Must furnish a mechanism for recovering the database
in the event that the database is damaged in any way.
Authorization Services– Must furnish a mechanism to ensure that only
authorized users can access the database.
Functions of a DBMS Support for Data Communication
– Must be capable of integrating with communication software.
Integrity Services– Must furnish a means to ensure that both the data in the
database and changes to the data follow certain rules.
Services to Promote Data Independence– Must include facilities to support the independence of
programs from the actual structure of the database.
Utility Services– Should provide a set of utility services.
ANSI/SPARC Architecture
...EXTERNAL LEVEL(individual userview)
CONCEPTUAL LEVEL(community user view)
INTERNAL LEVEL(storage view)
External Level
Users’ view of the database Language
– Application programmer– End-user
External View– Logical record– Data authorized to view
External Schema
Conceptual Level
Community view of database Representation of entire information
content Conceptual schema
– definition of total database content ++– data independent
Internal Level
Low-level representation of entire database– occurrences
Describes how the data is stored in the database
Not physical level Level used by utilities to increase
performance.
Data Model
Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.
Data Model comprises:– A structural part
– A manipulative part
– Possibly a set of integrity rules
Data Models Object-based Data Models
– Entity-Relationship– Semantic– Functional– Object-Oriented
Record-based Data Models– Relational Data Model– Network Data Model– Hierarchical Data Model
Physical Data Models
Back EndServer
Data Shared DBMS Database information Fat server vs thin server Should server contain
applications?
Middleware
Enables front end to speak to back end. Middleware can be as simple as API’s and
as complex as Tuxedo software Determinants
– variety of databases– networks– size