introduction & history of dbms
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TRANSCRIPT
SETHU.P.M
SJCET SCHOOL OF MANAGEMENT ,PALAI
Introduction and history of DBMS
File Based Data Management
Disadvantages of File based system
Why Use a DBMS?
Data independence and efficient access.
Reduced application development time.
Data integrity and security.
Uniform data administration.
Concurrent access, recovery from crashes.
A Database management systems (DBMS) is collection of programs that enables users to create and maintain a database. The DBMS is general purpose software system that facilitates the processes of defining, constructing, manipulating and sharing database among various users and application.
DefiningDefining a database involves specifiying the data types, structures and constraints of the data to be stored in tthe database.
ConstructingConstructing the database is the process of storing the data on some storage medium that is controlled by the DBMS.
ManipulatingManipulating a database includes functions such as querying the database to retrieve specific data, updating the database to reflect changes in the miniworld and generating reports from the data.
SharingSharing a database allows multiple users and programs to access the database simultaneously.
Other important functions provided by the DBMS include protecting the database and maintaining it over a long period of time. Protection includes system and security protection.
A typical large database may have life cycle of many years, so the DBMS must be able to maintain the database system by allowing the system to evolve as requirements change over time.
Benefits of DBMSReduction in Data Redundancy.
Reduction in Inconsistency.
Sharing of Data.
Enforcement of Standards.
Improvement of Data Security.
Maintenance of Data Integrity.
Better Interaction with Users.
Efficient System.
Purpose of Database Systems
Data redundancy and inconsistency Difficulty in accessing data Data isolation – multiple files and formats Integrity problems Atomicity of updates Concurrent access by multiple users Security problems
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Database management systems were developed to handle the following difficulties of typical file-processing systems supported by conventional operating systems:
Database Systems: A Brief Timeline
Ancient Times: RAM
was expensive and limited,
programmer productivity low.
1968 File-Based: Data
maintained in a flat file.
Programmer Defined both logical & physical structure, such as storage structure, access methods, I/O modes etc.
1968-1980 Era of non-relational database: IBM’s first hierarchical DBMS
called IMS. CODASYL DBTG model was for N/w. IDMS most popular
network DBMS.
1980-present Era of relational database
and Database Management System
(DBMS):
Processing characteristics determined by common use of magnetic tape medium
1970: Ted Codd at IBM’s San Jose Lab proposed relational models.
Two major projects start and both were operational in late 1970s o INGRES at University of California, Berkeley became
commercial and followed up POSTGRES which was incorporated into Informix.
o System R at IBM san Jose Lab, later evolved into DB2, which became one of the first DBMS product based on the relational model. (Oracle produced a similar product just prior to DB2.)
1976: Peter Chen defined the Entity-relationship(ER) model 1980s: Maturation of the relational database technology, more
relational based DBMS were developed and SQL standard adopted by ISO and ANSI.
Database Systems
1985: Object-oriented DBMS (OODBMS) develops. Little success commercially because advantages did not justify the cost of converting billions of bytes of data to new format
1990s: Incorporation of object-orientation in relational DBMSs, new application areas, such as data warehousing and OLAP, web and Internet, Interest in text and multimedia, enterprise resource planning (ERP) and management resource planning (MRP)
1991: Microsoft ships access, a personal DBMS created as element of Windows gradually supplanted all other personal DBMS products.
1995: First Internet database applications 1997: XML applied to database processing, which solves long-
standing database problems. Major vendors begin to integrate XML into DBMS products.
Components of a Database System
Four components: People, H/W, S/W, Data
Data: Data stored in a database include numerical data including whole numbers and floating- point numbers, and non numerical data such as characters , date, logical values.
Hardware: hardware of the system can range from to a network of computers .It also includes various storage devices and input and output devices.
Software : Software of a DBMS includes the DBMS, operating system , network software and the application programs.
Users : Three broad classes of users are considered.
1. Application programmer: Develop application programs.
2. End-Users : Access the database from a terminal using a query language.
3. Data Base Administrator (DBA): The design, construction and maintenance of a database.
Files vs. DBMS
Application must stage large datasets between main memory and secondary storage (e.g., buffering, page-oriented access, 32-bit addressing, etc.)
Special code for different queries Must protect data from inconsistency
due to multiple concurrent users Crash recovery Security and access control
Slide No:L1-5
Purpose of Database Systems
In the early days, database applications were built directly on top of file systems
Drawbacks of using file systems to store data
Data redundancy and inconsistency Multiple file formats, duplication of information in different files
Difficulty in accessing data Need to write a new program to carry out each new task
Data isolation — multiple files and formats
Integrity problems Integrity constraints (e.g. account balance > 0) become “buried” in program code rather than being
stated explicitly
Hard to add new constraints or change existing ones
Concurrent access by multiple usersConcurrent accessed needed for performance.Uncontrolled concurrent accesses can lead to inconsistencies.
Example: Two people reading a balance and updating it at the same time.
Atomicity of updatesFailures may leave database in an inconsistent state with partial updates carried out.Example: Transfer of funds from one account to another should either complete or not happen at all.
Security problemsHard to provide user access to some, but not all, data.
Types of DatabasesSingle-user: Supports only one user at a time.Desktop: Single-user database running on a personal
computer.Multi-user: Supports multiple users at the same time.Workgroup: Multi-user database that supports a small
group of users or a single department.Enterprise: Multi-user database that supports a large group
of users or an entire organization.Can be classified by location:
◦ Centralized: Supports data located at a single site.◦ Distributed: Supports data distributed across several
sites.
DATA LANGUAGES
The database provides a Data DefinitionLanguage to specify the database schema and a Data Manipulation Language to express database queries and updates.
• DATA-DEFINITION LANGUAGE (DDL)
• DATA-MANIPULATION LANGUAGE (DML)
STORAGE DEFINITION LANGUAGE (SDL) VIEW DEFINITION LANGUAGE (VDL)
Data-Definition Language (DDL)
We specify a database schema by a set of definition expressed by a special language called a Data-Definition Language.
DDL is used to create and delete database and its objects. These commands are primarily used by the DBA during the building and removal phases of a database project.
Ex: ALTER, DROP, TRUNCATE, COMMENT, RENAME
Data Manipulation Language (DML)
Language for accessing and manipulating the data organized by the appropriate data model.
DML also known as query language
• The retrieval of information stored in the database.• The insertion of new information into the database.• The deletion of information from the database.• The modification of information stored in the database. Two classes of languages
Procedural – user specifies what data is required and how to get those data
Nonprocedural – user specifies what data is required without specifying how to get those data
Database Administrator
Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs:
Database administrator’s duties include: Schema definition Storage structure and access method definition Schema and physical organization modification Granting user authority to access the database Specifying integrity constraints Acting as liaison with users Monitoring performance and responding to changes in
requirements
Database Users Users are differentiated by the way they expect to
interact with the system. Application programmers: interact with system
through DML calls. Specialized users: write specialized database
applications that do not fit into the traditional data processing framework
Sophisticated users: form requests in a database query language.
Naive users: invoke one of the permanent application programs that have been written previously
Advantages of DBMS• Data independence
•Application programs should not, ideally, be exposed to details of data representation and storage.
• Efficient Data access
•A DBMS uses several powerful functions to store and retrieve data efficiently
•Data Integrity and Security
•The DBMS enforces integrity constraints to get a kind of protection against prohibited access to data.
Advantages of DBMS
• Data Administration
When any users share the data, centralizing the administration of data can offer significant improvements.
• Concurrent Access and Crash Recovery
A DBMS schedules concurrent access to the data in such manner that users can think of the data as being accessed by only one user at a time. DBMS also protects users from the effects of system failures.
• Reduced Application Development Time
DBMS includes several important functions that are common to many applications accessing data in the DBMS. In conjunction with the high-level interface to the data, facilitates quick application development.
Disadvantages of DBMSa. Complexity.b. Size.c. Technical experts are required .d. Cost of DBMS development .e. Additional hardware costs.f. Performance monitoring & maintenance .g. Higher impact of a failure.h. Centralization: That is use of the same program at a time by many user sometimes
lead to loss of some data.i. Limited Statistical Capabilities: Can not perform sophisticated calculations
Security issues.
Summary Data are raw facts. Information is the result of processing data to reveal its
meaning. To implement and manage a database, use a DBMS. Database design defines the database structure. A well-designed database facilitates data management and generates
accurate and valuable information. A poorly designed database can lead to bad decision making, and bad
decision making can lead to the failure of an organization. Databases were preceded by file systems. Limitations of file system data management:
requires extensive programming. system administration complex and difficult. making changes to existing structures is difficult. security features are likely to be inadequate. independent files tend to contain redundant data.
DBMS’s were developed to address file systems’ inherent weaknesses.
