Chapter 1 2 Introduction to Databases Transparencies CS
Chapter 1, 2 Introduction to Databases Transparencies CS 424 Introduction of Database System
Chapter 1 - Objectives Some common uses of database systems. l Characteristics of file-based systems. l Problems with file-based approach. l Meaning of the term database. l Meaning of the term Database Management System (DBMS). l CS 424 Introduction of Database System
Chapter 1 - Objectives Typical functions of a DBMS. l Major components of the DBMS environment. l Personnel involved in the DBMS environment. l History of the development of DBMSs. l Advantages and disadvantages of DBMSs. l CS 424 Introduction of Database System
Examples of Database Applications Purchases from the supermarket l Purchases using your credit card l Booking a holiday at the travel agents l Using the local library l Taking out insurance l Renting a video l Using the Internet l Studying at university l CS 424 Introduction of Database System
File-Based Systems l Collection of application programs that perform services for the end users (e. g. reports). l Each program defines and manages its own data. CS 424 Introduction of Database System
Files Base Process CS 424 Introduction of Database System
File-Based Processing 1. Reading data from computer which scan the X-Ray 2. Weather data to be analyzed 3. The software which can read certain data and give you the output CS 424 Introduction of Database System
Limitations of File-Based Approach l Separation and isolation of data Each program maintains its own set of data. l Users of one program may be unaware of potentially useful data held by other programs. l l Duplication of data Same data is held by different programs. l Wasted space and potentially different values and/or different formats for the same item. l CS 424 Introduction of Database System
Limitations of File-Based Approach l Data dependence l l Incompatible file formats l l File structure is defined in the program code. Programs are written in different languages, and so cannot easily access each other’s files. Fixed Queries/Proliferation of application programs l l Programs are written to satisfy particular functions. Any new requirement needs a new program. CS 424 Introduction of Database System
Database Approach l Arose because: l l l Definition of data was embedded in application programs, rather than being stored separately and independently. No control over access and manipulation of data beyond that imposed by application programs. Result: l the database and Database Management System (DBMS). CS 424 Introduction of Database System
Database Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization. l System catalog (metadata) provides description of data to enable program– data independence. l Logically related data comprises entities, attributes, and relationships of an organization’s information. l CS 424 Introduction of Database System
Database Management System (DBMS) l A software system that enables users to define, create, maintain, and control access to the database. l (Database) application program: a computer program that interacts with database by issuing an appropriate request (SQL statement) to the DBMS. CS 424 Introduction of Database System
Database Management System (DBMS) CS 424 Introduction of Database System
Database Approach l Data definition language (DDL). l l l Permits specification of data types, structures and any data constraints. All specifications are stored in the database. Data manipulation language (DML). l General enquiry facility (query language) of the data. CS 424 Introduction of Database System
Database Approach l Controlled access to database may include: l a security system l an integrity system l a concurrency control system l a recovery control system l a user-accessible catalog. CS 424 Introduction of Database System
Views l Allows each user to have his or her own view of the database. l A view is essentially some subset of the database. CS 424 Introduction of Database System
Views - Benefits Reduce complexity l Provide a level of security l Provide a mechanism to customize the appearance of the database l Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed l CS 424 Introduction of Database System
Components of DBMS Environment CS 424 Introduction of Database System
Components of DBMS Environment l Hardware l l Software l l Can range from a PC to a network of computers. DBMS, operating system, network software (if necessary) and also the application programs. Data l Used by the organization and a description of this data called the schema. CS 424 Introduction of Database System
Components of DBMS Environment l Procedures l l Instructions and rules that should be applied to the design and use of the database and DBMS. People CS 424 Introduction of Database System
Components of Database Management System (DBMS) CS 424 Introduction of Database System
DBMS Architecture CS 424 Introduction of Database System
DBMS Architecture l The Internal or Physical Level: l l l The collection of files permanently stored on secondary storage devices. And it provides a low-level description of the physical database, and an interface between the operating system's file system and the record structures used in higher levels of abstraction. At this level record types and methods of storage are defined, as well as how stored fields are represented. CS 424 Introduction of Database System
DBMS Architecture l The Conceptual Level: l l l It presents a logical view of the entire database, which allows you to bring all the data in the database together and see it in a consistent manner. The first stage in the design of a database is to define the conceptual view, and a DBMS provides a data definition language DDL for this purpose. The data definition language used to create the conceptual level must not specify any physical storage considerations that should be handled by the physical level. It should not provide any storage or access details, but should define the information content only. CS 424 Introduction of Database System
DBMS Architecture l The External or View Level: l l l It provides a window on the conceptual view which allows the user to see only the data of interest to them. The user can be either an application program or an end user. Any number of external views can be defined and they can overlap each other. The System Administrator and the DBA are special cases. Because they have responsibilities for the design and maintenance of the database, they at times need to be able to see the entire database. The external and the conceptual view are functionally equivalent for these two users. CS 424 Introduction of Database System
Roles in the Database Environment l Data Administrator (DA) l Database Administrator (DBA) l Database Designers (Logical and Physical) l Application Programmers l End Users (naive and sophisticated) CS 424 Introduction of Database System
History of Database Systems l First-generation l l Second generation l l Hierarchical and Network Relational Third generation l l Object-Relational Object-Oriented CS 424 Introduction of Database System
DBs Hierarchical 1960 s l l l The hierarchical data model organizes data in a tree structure. There is a hierarchy of parent and child data segments. This structure implies that a record can have repeating information, generally in the child data segments. Data in a series of records, which have a set of field values attached to it. It collects all the instances of a specific record together as a record type. These record types are the equivalent of tables in the relational model, and with the individual records being the equivalent of rows. To create links between these record types, the hierarchical model uses Parent Child Relationships. These are a 1: N mapping between record types. This is done by using trees, CS 424 Introduction of Database System
DBs Network 1970 s • data were more naturally modeled with more than one parent per child. • So, the network model permitted the modeling of many-to-many relationships in data • The basic data modeling construct in the network model is the set construct. • A set consists of an owner record type, a set name, and a member record type. A member record type can have that role in more than one set CS 424 Introduction of Database System
Advantages of DBMSs Control of data redundancy l Data consistency l More information from the same amount of data l Sharing of data l Improved data integrity l Improved security l Enforcement of standards l Economy of scale l CS 424 Introduction of Database System
Advantages of DBMSs Balance conflicting requirements l Improved data accessibility and responsiveness l Increased productivity l Improved maintenance through data independence l Increased concurrency l Improved backup and recovery services l CS 424 Introduction of Database System
Disadvantages of DBMSs Complexity l Size l Cost of DBMS l Additional hardware costs l Cost of conversion l Performance l Higher impact of a failure l CS 424 Introduction of Database System
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