Section 05Concepts Of DBMS1 HSQ - DATABASES & SQL And Franchise Colleges 05 Concepts of DBMS By MANSHA NAWAZ

Section 05Concepts Of DBMS2 Introduction In this lecture we will be looking at some of the fundamental concepts behind a Database Management System (DBMS). –RDBMS - Relational DBMS Exploring the Advantages and Disadvantages of using a DBMS Exploring the Architecture of a DBMS and some of the associated issues.

Section 05Concepts Of DBMS3 Advantages of the DBMS Approach The Database Approach Versus the Traditional File Processing Approach –Storing data in a non-redundant database improves consistency of data. There is only one copy of each item of data. Unproductive Maintenance avoided. –In file based systems, changes to file structure cause endless problems on maintenance (re-writing code). –Using a DBMS, program access is through a limited view (using SQL). Thus programs can’t see minor changes to the database. We will be exploring data independence in more detail later.

Section 05Concepts Of DBMS4 Some of the Advantages of using a DBMS  Sharing of data  Control of redundancy and thus Data consistency  Improved data integrity  Better data accessibility  Representing complex relationships among data  Enforcing integrity constraints  Better security of data (as long as backup is perfect)  More control over concurrency  Better backup and recovery procedures  Providing multiple interfaces  Faster development of new applications  Economy of scale

Section 05Concepts Of DBMS5 Some of the Disadvantages of using a DBMS  High cost of Software  Hardware costs high due to software complexity  Requirement for skilled staff  Higher programming costs - greater skill required  Slower processing of some applications  Increased vulnerability (all your eggs in one basket)  More difficult recovery (if disaster strikes)

Section 05Concepts Of DBMS6 DBMS Architecture Usually taken to imply a three level architecture. The complexity of a large database is handled by a DBMS by providing three views of the data. –An internal view of how the data is stored and accessed –A conceptual view of what data is available in the database. –Local or external views which are a limited and simplified view of the database as suitable for a single application or group of associated applications. Data abstraction –Users deal with conceptual representation of the data. –They have little control over how the data is stored.

Section 05Concepts Of DBMS7 Three Level Architecture External Level View 1 View 4 View 2 View 3 et c. Conceptual Level Conceptual Schema Internal Schema Internal Level Physical Data Independence Logical Data Independence One of the fundamental aspects of the database approach using a DBMS is that, by providing levels of data abstraction, it hides complexity of data storage from users. ERD - Logical View ERD - Table View

Section 05Concepts Of DBMS8 Database schema - the description of a database Schema - a description of a database in terms that a DBMS understands External Schema –A database system may have several external schemas each suitable for a single application or group of associated applications. –They provide a means of limiting the perceived complexity of a large system. –Hide those parts of the database which are not required for a particular purpose or department (useful security). –External schemas are based on the conceptual schema. –Each external schema describes a section of the database of interest to a particular group of users (or programs).

Section 05Concepts Of DBMS9 Client/Server Architecture User Workstation Operator Workstation Department File-Servers Corporate Servers Server provides services for the Clients which are responsible for interacting with the users (Input/Output) Server is responsible for performing a service (e.g. transaction) and guaranteeing the integrity of the data Well suited for distributed systems handling large amounts of data

Section 05Concepts Of DBMS10 E-R Model NF Systems Analysis & Design DFD DataStores, DataFlows and Data Dictionary DBMS PHYSICAL VIEW OF DATA TABLES LOGICAL VIEW OF DATA FORMS DATA MODEL TABLE SET Database connectivity via websites technology Macromedia Dreamweaver MS Visual Studio Database connectivity via desktop DBMS such as MS Access Database connectivity via programming languages such as MS Visual Basic Area of Interest Database Development

Section 05Concepts Of DBMS11 End of Lecture