Introduction Database Concepts

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1 Introduction Database Concepts CO attained : CO1 Hours Required: 05 Self Study: 08 Prepared and presented by : Ms. Swati Abhang

2 Contents Introduction Characteristics of databases, File system V/s Database system, Users of a Database system Data Models, Schemas, and Instances, Three-Schema Architecture and Data Independence, Database Administrator (DBA), Role of a DBA

3 What is a Database System? DBMS Application program End-user 1-3

4 What is a DATABASE? Definition A database is a well organized collection of data that are related in meaningful way which can be accessed in a different logical orders but are stored only once. The data in the database is therefor integrated, structured and shared.

5 What is a Database System? (cont.) Major components of a database system: Data: integrated and shared. Hardware: disk, CPU, Main Memory,... Software: DBMS Users: 1. Application programmers 2. End users 3. Database administrator (DBA) Defining external schema Defining conceptual schema Defining internal schema Liaison with users Defining security and integrity checks Defining backup and recovery procedures Monitoring performance and changing requirements 1-5

6 Why Database? Redundancy can be reduced Inconsistency can be avoided The data can be shared Standards can be enforced Security restrictions can be applied Integrity can be maintained Provision of data independence objective! 1-6

7 Characteristics of databases Persistent Data Metadata and self-describing Nature Data Independence Access flexibility and Security

8 Characteristics of dbms To incorporate the requirements of the organization, system should be designed for easy maintenance. Information systems should allow interactive access to data to obtain new information without writing fresh programs. System should be designed to co-relate different data to meet new requirements. An independent central repository, which gives information and meaning of available data is required. 1-8

9 Characteristics of dbms Integrated database will help in understanding the interrelationships between data stored in different applications. The stored data should be made available for access by different users simultaneously. Automatic recovery feature has to be provided to overcome the problems with processing system failure. 1-9

10 Functions of the DBMS Data Definition Language (DDL) Data Manipulation Language (DML) Data Security and Integrity Data Recovery and Concurrency Data Dictionary Performance 1-10

11 History of Database Systems 1950s and early 1960s: Data processing using magnetic tapes for storage Tapes provided only sequential access Punched cards for input Late 1960s and 1970s: Hard disks allowed direct access to data Network and hierarchical data models in widespread use Ted Codd defines the relational data model Would win the ACM Turing Award for this work IBM Research begins System R prototype UC Berkeley begins Ingres prototype High-performance (for the era) transaction processing

12 History (cont.) 1980s: Research relational prototypes evolve into commercial systems SQL becomes industrial standard Parallel and distributed database systems Object-oriented database systems 1990s: Large decision support and data-mining applications Large multi-terabyte data warehouses Emergence of Web commerce Early 2000s: XML and XQuery standards Automated database administration Later 2000s: Giant data storage systems Google BigTable, Yahoo PNuts, Amazon,..

13 Database: Historical Roots Manual File System to keep track of data used tagged file folders in a filing cabinet organized according to expected use e.g. file per customer easy to create, but hard to locate data aggregate/summarize data Computerized File System to accommodate the data growth and information need manual file system structures were duplicated in the computer Data Processing (DP) specialists wrote customized programs to write, delete, update data (i.e. management) extract and present data in various formats (i.e. report) 13 S511 Session 2, IU-SLIS

14 File System: Example Database Systems: Design, Implementation, & Management: Rob & Coronel 14 S511 Session 2, IU-SLIS

15 File System: Weakness Weakness Islands of data in scattered file systems. Problems Duplication same data may be stored in multiple files Inconsistency same data may be stored by different names in different format Rigidity requires customized programming to implement any changes cannot do ad-hoc queries Implications Waste of space Data inaccuracies High overhead of data manipulation and maintenance 15 S511 Session 2, IU-SLIS

16 File System: Problem Case CUSTOMER file AGENT file SALES file A_Name (15 char) Carol Johnson A_Name (20 char) Carol T. Johnson AGENT (20 char) Carol J. Smith - inconsistent field name, field size - inconsistent data values - data duplication 16 S511 Session 2, IU-SLIS

17 Database System vs. File System Database Systems: Design, Implementation, & Management: Rob & Coronel 17 S511 Session 2, IU-SLIS

18 Hierarchical Database Background Developed to manage large amount of data for complex manufacturing projects e.g., Information Management System (IMS) IBM-Rockwell joint venture clustered related data together hierarchically associated data clusters using pointers Hierarchical Database Model Assumes data relationships are hierarchical One-to-Many (1:M) relationships Each parent can have many children Each child has only one parent Logically represented by an upside down tree 18 S511 Session 2, IU-SLIS

19 Hierarchical Database: Example Database Systems: Design, Implementation, & Management: Rob & Coronel 19 S511 Session 2, IU-SLIS

20 Hierarchical Database: Pros & Cons Advantages Conceptual simplicity groups of data could be related to each other related data could be viewed together Centralization of data reduced redundancy and promoted consistency Disadvantages Limited representation of data relationships did not allow Many-to-Many (M:N) relations Complex implementation required in-depth knowledge of physical data storage Structural Dependence data access requires physical storage path Lack of Standards limited portability 20 S511 Session 2, IU-SLIS

21 Data Manipulation Language (DML) Language for accessing and manipulating the data organized by the appropriate data model DML also known as query language Two classes of languages Procedural user specifies what data is required and how to get those data Declarative (nonprocedural) user specifies what data is required without specifying how to get those data SQL is the most widely used query language

22 Data Definition Language (DDL) Specification notation for defining the database schema Example: create table account ( account_number branch_name balance char(10), char(10), integer) DDL compiler generates a set of tables stored in a data dictionary Data dictionary contains metadata (i.e., data about data) Database schema Data storage and definition language Specifies the storage structure and access methods used Integrity constraints Domain constraints Referential integrity (e.g. branch_name must correspond to a valid branch in the branch table) Authorization

23 Users of Database system

24 Database Users Database Administrators In a database environment, the primary resource is the database itself and the secondary resource is the DBMS and related software authorizing access to the database coordinating and monitoring its use acquiring software and hardware resources as needed Database Designers identifying the data to be stored in the database choosing appropriate structures to represent and store this data undertaken before the database is actually implemented and populated with data

25 Database Users.. communicate with all prospective database users, in order to understand their requirements develop a view of the database that meets the data and processing requirements for each group of users These views are then analyzed and integrated with the views of other user groups. The final database design must be capable of supporting the requirements of all user groups End Users access to the database for querying, updating, and generating reports Casual end users: occasionally access the database need different information each time learn only a few facilities that they may use repeatedly.

26 Database Users.. use a sophisticated database query language to specify their requests typically middle- or high-level managers or other occasional browsers Naive or parametric end users constantly querying and updating the database, using standard types of queries and updates called canned transactions that have been carefully programmed and tested need to learn very little about the facilities provided by the DBMS Bank tellers check account balances and post withdrawals and deposits Reservation clerks for airlines, hotels, and car rental companies check availability for a given request and make reservations Clerks at receiving stations for courier mail enter package identifications via bar codes and descriptive information through buttons to update a central database of received and in-transit packages

27 Database Users.. Sophisticated end users Engineers, scientists, business analysts, and others who thoroughly familiarize themselves with the facilities of the DBMS so as to implement their applications to meet their complex requirements Try to learn most of the DBMS facilities in order to achieve their complex requirements Stand-alone users Maintain personal databases by using ready-made program packages that provide easy-to-use menu- or graphics-based interfaces. An example is the user of a tax package that stores a variety of personal financial data for tax purposes Typically become very proficient in using a specific software package

28 Database Users.. System Analysts and Application Programmers Determine the requirements of end users, especially naive and parametric end users, and develop specifications for canned transactions that meet these requirements Application programmers implement these specifications as programs; then they test, debug, document, and maintain these canned transactions Workers behind the Scene Typically do not use the database for their own purposes DBMS system designers and implementers design and implement the DBMS modules (for implementing the catalog, query language, interface processors, data access, concurrency control, recovery, and security. ) and interfaces as a software package

29 Database Users.. Tool developers Tools are optional packages that are often purchased separately include packages for database design, performance monitoring, natural language or graphical interfaces, prototyping, simulation, and test data generation. Operators and maintenance personnel system administration personnel who are responsible for the actual running and maintenance of the hardware and software environment for the database system

30 Data Models A collection of tools for describing Data Data relationships Data semantics Data constraints Relational model Entity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Objectrelational) Semistructured data model (XML) Other older models: Network model Hierarchical model

31 Relational Model All the data is stored in various tables. Example of tabular data in the relational model Columns Rows

32 A Sample Relational Database

33 Instances and Schemas Similar to types and variables in programming languages Logical Schema the overall logical structure of the database Example: The database consists of information about a set of customers and accounts in a bank and the relationship between them Analogous to type information of a variable in a program Physical schema the overall physical structure of the database Instance the actual content of the database at a particular point in time Analogous to the value of a variable Physical Data Independence the ability to modify the physical schema without changing the logical schema Applications depend on the logical schema In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.

34 Architecture of DBMS Following are the three levels of database architecture, 1. Physical Level 2. Conceptual Level 3. External Level

35 Three Levels Architecture of DBMS

36 Mapping is the process of transforming request response between various database levels of architecture. Mapping is not good for small database, because it takes more time. In External / Conceptual mapping, DBMS transforms a request on an external schema against the conceptual schema. In Conceptual / Internal mapping, it is necessary to transform the request from the conceptual to internal levels.

37 1. Physical Level Physical level describes the physical storage structure of data in database. It is also known as Internal Level. This level is very close to physical storage of data. At lowest level, it is stored in the form of bits with the physical addresses on the secondary storage device. At highest level, it can be viewed in the form of files. The internal schema defines the various stored data types. It uses a physical data model.

38 2. Conceptual Level Conceptual level describes the structure of the whole database for a group of users. It is also called as the data model. Conceptual schema is a representation of the entire content of the database. These schema contains all the information to build relevant external records. It hides the internal details of physical storage.

39 3. External Level External level is related to the data which is viewed by individual end users. This level includes a no. of user views or external schemas. This level is closest to the user. External view describes the segment of the database that is required for a particular user group and hides the rest of the database from that user group.

40 Architec ture of DBMS /Databa se System Internal s

42 Responsibilities of DBA Installation, configuration and upgradation of databases like Microsoft SQL/ MySQL/ Oracle Server Software. Evaluating the features of various databases. Establishing and maintaining sound backup and recovery policies and procedures. Taking care of database design and implementation. Implementing and maintaining the database security. Database tuning, application tunning and performance monitoring. Maintaining documentation and standards. DBA does some technical trouble shooting and consultation to development teams.

43 Skill set is required to be a successful Database Administrator Problem Management Incident Management Chain Management Capacity Planning

44 Types of DBA 1. Administrative DBA 2. Development DBA 3. Architect 4. Data Warehouse DBA 5. OLAP DBA

45 Types of DBA 1. Administrative DBA Administrative DBA maintains the work on the server and keeps it running. Administrative DBA is mostly concerned with backups, security, replication etc. 2. Development DBA Development DBA builds queries, stored procedures etc. which mostly meet business needs. Development DBA is equivalent to a programmer.

46 Types of DBA 3. Architect Architect builds table, design schema, foreign keys, primary keys etc. which meets the business needs. 4. Data Warehouse DBA Data Warehouse DBA is responsible for merging the data from multiple sources into a data warehouse. 5. OLAP DBA OLAP DBA builds multi-dimensional cubes for decision support or OLAP systems. The primary language in SQL Server is MDX.

47 Important Questions 1. What is a database? Discuss its main features and explain the importance of each feature. 2. List the characteristics of databases. 3. Describe the disadvantages of using a file processing system compared to a database system? 4. What is DBMS? What task does a DBMS carry out? 5. What are classes of users use database systems? 6. List three views for database system in three level architecture. Describe role of these views. 7. List the major components of DBMS architecture and describe their functions. 8. Describe role of DBA

48 What is meant by logical and physical structure of data? Explain difference between logical and physical independence? Explain difference between external, internal and conceptual view in three-tier database architecture. How are these different schema layers related to the concept of logical and physical data independence.

Chapter 1: Introduction

Chapter 1: Introduction Chapter 1: Introduction Purpose of Database Systems Database Languages Relational Databases Database Design Data Models Database Internals Database Users and Administrators Overall