dbms
TRANSCRIPT
Problems with file processing systemsInconsistent dataInflexibilityLimited data sharingPoor enforcement of standardsExcessive program maintenance
Levels of DataCharacter :The most basic logical element is character.Which
consists of alphabetic, numeric or other symbol.Field : It consists of grouping of characters.For example, the
grouping of alphabetic characters.For example grouping of alphabetic characters in a person’s name form a name field.
Record :Related fields of data are grouped to form a record.File :A group of related records is a data file, or table.Database :The highest level in the hierarchy is the database.A
database is an integrated collection of logically related records or files.
Objectives of Data BaseControlled RedundancyEase of learning and useData independenceAccuracy and IntegrityPrivacy and securitySharedRecovery from failurePerformance
Types of Data BasesOperational Data Base Analytical Data BaseData Warehouse Data BaseDistributed Data BaseEnd User Data BaseExternal Data Base
Operational DatabaseData Bases store detailed data needed to support operations of
entire organizationThey are also called Subject Area Databases ,transaction
database and production databaseA customer database, inventory database, and other database
containing data generated by business operations
Analytical DatabaseDatabases store data extracted from selected operational and
external databasesConsists of data mostly needed by an organization’s managers
and other end users They are also called management databases or information
databasesThey are the databases accessed by the online analytical
processing (OLAP) systems, decision support systems and executive information systems
Data Warehouse DatabasesStores data from current and previous years that has been
extracted from various operational and analytical databases of an organization
It is a central source of data that has been standardized and integrated so it can be used by managers and other end user professionals throughout an organization
Distributed DatabaseDatabases of local work groups and departments at regional
offices, branch offices, manufacturing plants and other work sites
Can include segments of common operational and common user databases as well as data generated and used only at a user’s own site
Ensuring that all the data in distributed databases are consistently and concurrently updated
End User DatabaseThese databases consist of a variety of data files developed by
end users at their workstations For example, users may have their own electronic copies of
documents they generated with word processing packages or received by electronic mail.
External DatabaseAccess to external online databases or data banks is available
for a fee from commercial information services , or for free of price from many sources on the internet
For example, data are available in the form of statistics on economic and demographic activity from statistical data banks
Abstracts from newspapers, magazines, and other periodicals from bibliographic data banks
Database Management System
DBMS is the software that permits an organization to centralize data, manage them efficiently, and provide access to the stored data by application programs .
DBMS acts as an interface between the application program and the physical data files
DBMS has three components A data definition language A data manipulation language A data dictionary
Data Definition Language The data definition language is the formal language used by
the programmers to specify the content and structure of database
It defines each data element as it appears in the database before that data element is translated into the forms required by application programs
Data Manipulation LanguageThis language contains commands that permits end users and
programmers to extract data from the database to satisfy information requests and develop applications
The most prominent data manipulation language today is structured query language (SQL)
Data DictionaryThis is an automated or manual file that stores definitions of
data elements and data characteristics such as usage, physical representation, ownership, authorization and security
Many data dictionaries can produce lists and reports of data utilization, groupings, program location and so on
Functions of DBMSOrganizes dataIntegrates dataSeparates dataControls dataRetrieves dataProtects data
Benefits of DBMSReduced programming costsReduced development and implementation timeReduced program and file maintenance costsReduced data RedundancyIncrease flexibility
Data Storage and Retrieval
Data is not stored in a random fashion. It is organized for efficient retrieval.
Sequential organizationIndexed Sequential OrganizationInverted List OrganizationDirect Access Organization
Sequential OrganizationIt simply means storing and sorting in physical, contiguous
blocks within files on tape or diskRecords are also in sequence within each blockIt is best suited in reading one record after another without a
search delayThe records can be added only at the end of the file
Indexed Sequential OrganizationData is stored in physically contiguous blocks and uses indexes
to locate records Indexed Sequential Organization reduces the magnitude of the
sequential search and provides quick access for sequential and direct processing
The drawback is the extra storage space required for the index. It also takes long to search the index for data access or retrieval
Inverted List OrganizationIt differ from the previous in the index level and record storageThe indexed sequential method has a multiple index for a
given key, whereas the inverted list method has a single index for each key type
In inverted list records are not needed to be stored in a particular sequence. They are placed in data storage area but indexes are updated for the record keys and location
Inverted lists are best for applications that request specific data on multiple keys
Direct Access OrganizationIn direct access file organization, records are placed randomly
throughout the file New records are added at the end of the file or inserted in
specific locations based on software commandsRecords are accessed by addresses that specify their disk
locations. An address is required for locating a record, for linking records , or for establishing relationships
Hierarchical Data Model
Employee
Job assignments BenefitsCompensation
Performance Salary hist Pension Life insurance Health
Network Data Model
Course 2Course 1 Course 3
Student 1 Student 2 Student 3 Student 4 Student 5 Student 6
Relational Data Model
Dept .no D name
D loc
Emp no
Dep. A
Dep. B
Dep. C
Emp. no
E name
E title
E sal
Dep. no
E1 D A
E2 D A
E3 D B
E4 D B
E5 D C
E6 D A
Data Schemes The schemes (schema) define categories of data and their
properties .External Schema or user schema is the user’s view of a part
of the databaseConceptual Schema is the overall logical view of the databaseInternal Schema or data storage definition is the way the data
is physically organized in storage
General Model
External Schemas
User View
User View
User View
Conceptual Schema
InternalSchema
StoredDatabase
External SchemaEach user of the database (an application program or a person
formulating a query ) is concerned with only a small portion of the database
Each user is interested in only a part of the entities in the database, only part of the attributes of those entities, and certain relationships among the entities
External schema consists basically of definitions of each of the various external record types in the external view
The external schema is written using the DDL portion of the user’s data sub language
Conceptual SchemaThe conceptual schema is the logical view of the entire
database . It represents as closely as possible the real entities and their relationships .
It contains integrity rules and authorization rules, but it does not contain information about how the data items are stored
Internal SchemaThe internal schema or physical data model describes how the
database is organized for physical storage and access
The internal schema includes information on ordering of records, block sizes, storage indexes, use of pointers and access strategies being used
MappingA mapping is a transaction of one schema to anotherIn order for a user to access data, the user view of the data as
reflected in the external schema must be translated into the overall conceptual schema
In the same way, the conceptual/internal mapping translates logical descriptions of data in the conceptual schema to physical locations and access paths in the internal scheme