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Database Management Systems
UNIT -
1.0 Introduction and brief history to Database
1.1 Characteristics of database
1.2 Difference between File System & DBMS.
1.3 Advantages of DBMS
1.4 Functions of DBMS
1.5 Role of Database Administrator
1.6 Simplified Database System Environment
1.7 Example of a Database
1.8 Architecture of DBMS
1.9 Data Independence
1.10 Types of database applications
1.11 Data Models
1.12 The database system environment
1.13 Centralized and Client-Server DBMS Architectures
Introduction to Database
1.0 Introduction
Database is a collection of related data. Database management system is software designed to assist the maintenance and utilization of large scale collection of data. DBMS came into existence in 1960 by Charles. Integrated data store which is also called as the first general purpose DBMS. Again in 1960 IBM brought IMS-Information management system. In 1970 Edgor Codd at IBM came with new database called RDBMS. In 1980 then came SQL Architecture- Structure Query Language. In 1980 to 1990 there were advances in DBMS e.g. DB2, ORACLE.
Data
- Data is raw fact or figures or entity.
- When activities in the organization takes place, the effect of these activities need to be recorded which is known as Data.
Information
- Processed data is called information
- The purpose of data processing is to generate the information required for carrying out the business activities.
In general data management consists of following tasks
- Data capture: Which is the task associated with gathering the data as and when they originate.
- Data classification: Captured data has to be classified based on the nature and intended usage.
- Data storage: The segregated data has to be stored properly.
- Data arranging: It is very important to arrange the data properly
- Data retrieval: Data will be required frequently for further processing, Hence it is very important to create some indexes so that data can be retrieved
1.1 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.
- Integrated database will help in understanding the inter-relationships 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.
DBMS Utilities
- A data loading utility: Which allows easy loading of data from the external format without writing programs.
- A backup utility: Which allows to make copies of the database periodically to help in cases of crashes and disasters.
- Recovery utility: Which allows to reconstruct the correct state of database from the backup and history of transactions.
- Monitoring tools: Which monitors the performance so that internal schema can be changed and database access can be optimized.
- File organization: Which allows restructuring the data from one type to another?
1.2 Difference between File system & DBMS
File System
- File system is a collection of data. Any management with the file system, user has to write the procedures
- File system gives the details of the data representation and Storage of data.
- In File system storing and retrieving of data cannot be done efficiently.
- Concurrent access to the data in the file system has many problems like a. Reading the file while other deleting some information, updating some information
- File system doesn’t provide crash recovery mechanism. Eg. While we are entering some data into the file if System crashes then content of the file is lost.
- Protecting a file under file system is very difficult.
DBMS
- DBMS is a collection of data and user is not required to write the procedures for managing the database.
- DBMS provides an abstract view of data that hides the details.
- DBMS is efficient to use since there are wide varieties of sophisticated techniques to store and retrieve the data.
- DBMS takes care of Concurrent access using some form of locking.
- DBMS has crash recovery mechanism, DBMS protects user from the effects of system failures.
- DBMS has a good protection mechanism.
DBMS = Database Management System RDBMS = Relational Database Management System
1.4 Functions of DBMS
- Data Definition: The DBMS provides functions to define the structure of the data in the application. These include defining and modifying the record structure, the type and size of fields and the various constraints to be satisfied by the data in each field.
- Data Manipulation: Once the data structure is defined, data needs to be inserted, modified or deleted. These functions which perform these operations are part of DBMS. These functions can handle plashud and unplashud data manipulation needs. Plashud queries are those which form part of the application. Unplashud queries are ad-hoc queries which performed on a need basis.
- Data Security & Integrity: The DBMS contains modules which handle the security and integrity of data in the application.
- Data Recovery and Concurrency: Recovery of the data after system failure and concurrent access of records by multiple users is also handled by DBMS.
- Data Dictionary Maintenance: Maintaining the data dictionary which contains the data definition of the application is also one of the functions of DBMS.
- Performance: Optimizing the performance of the queries is one of the important functions of DBMS.
1.5 Role of Database Administrator.
Typically there are three types of users for a DBMS:
- The END User who uses the application. Ultimately he is the one who actually puts the data into the system into use in business. This user need not know anything about the organization of data in the physical level.
- The Application Programmer who develops the application programs. He/She has more knowledge about the data and its structure. He/she can manipulate the data using his/her programs. He/she also need not have access and knowledge of the complete data in the system.
- The Data base Administrator (DBA) who is like the super-user of the system.
The role of DBA is very important and is defined by the following functions.
- Defining the schema: The DBA defines the schema which contains the structure of the data in the application. The DBA determines what data needs to be present in the system and how this data has to be presented and organized.
- Liaising with users: The DBA needs to interact continuously with the users to understand the data in the system and its use.
- Defining Security & Integrity checks: The DBA finds about the access restrictions to be defined and defines security checks accordingly. Data Integrity checks are defined by the DBA.
- Defining Backup/Recovery Procedures: The DBA also defines procedures for backup and recovery. Defining backup procedure includes specifying what data is to be backed up, the periodicity of taking backups and also the medium and storage place to backup data.
- Monitoring performance: The DBA has to continuously monitor the performance of the queries and take the measures to optimize all the queries in the application.
1.7 Example of a Database (with a Conceptual Data Model)
- Mini-world for the example: Part of a UNIVERSITY environment.
- Some mini-world entities: STUDENTs COURSEs SECTIONs (of COURSEs) (academic) DEPARTMENTs INSTRUCTORs
Example of a Database (with a Conceptual Data Model)
- Some mini-world relationships: SECTIONs are of specific COURSEs STUDENTs take SECTIONs COURSEs have prerequisite COURSEs INSTRUCTORs teach SECTIONs COURSEs are offered by DEPARTMENTs STUDENTs major in DEPARTMENTs
Example of a simple Database
Example of a Student File
Example of a simplified database catalog
1.8 Architecture of DBMS
conceptual view of the database. The conceptual view is the overall community view of the database and it includes all the information that is going to be represented in the database. The conceptual view is defined by the conceptual schema which includes definitions of each of the various types of data.
The internal view is the view about the actual physical storage of data. It tells us what data is stored in the database and how. At least the following aspects are considered at this level:
Storage allocation e.g. B-trees, hashing etc. Access paths e.g. specification of primary and secondary keys, indexes and pointers and sequencing. Miscellaneous e.g. data compression and encryption techniques, optimization of the internal structures.
Efficiency considerations are the most important at this level and the data structures are chosen to provide an efficient database. The internal view does not deal with the physical devices directly. Instead it views a physical device as a collection of physical pages and allocates space in terms of logical pages.
The separation of the conceptual view from the internal view enables us to provide a logical description of the database without the need to specify physical structures. This is often called physical data independence. Separating the external views from the conceptual view enables us to change the conceptual view without affecting the external views. This separation is sometimes called logical data independence.
Assuming the three level view of the database, a number of mappings are needed to enable the users working with one of the external views. For example, the payroll office may have an external view of the database that consists of the following information only: Staff number, name and address.
Staff tax information e.g. number of dependents. Staff bank information where salary is deposited. Staff employment status, salary level, leave information etc.
The conceptual view of the database may contain academic staff, general staff, casual staff etc. A mapping will need to be created where all the staff in the different categories are combined into one category for the payroll office. The conceptual view would include information about each staff's position, the date employment started, full-time or part- time etc. This will need to be mapped to the salary level for the salary office. Also, if there is some change in the conceptual view, the external view can stay the same if the mapping is changed.
1.9 Data Independence
Data independence can be defined as the capacity to change the schema at one level without changing the schema at next higher level. There are two types of data Independence. They are
- Logical data independence.
- Physical data independence.
- Logical data independence is the capacity to change the conceptual schema without having to change the external schema.
- Physical data independence is the capacity to change the internal schema without changing the conceptual schema.
When not to use a DBMS
- Main inhibitors (costs) of using a DBMS:
- High initial investment and possible need for additional hardware.
- Overhead for providing generality, security, concurrency control, recovery, and integrity functions When a DBMS may be unnecessary:
relationships
constraints
Types of Data Models
- High Level- Conceptual data model.
- Low Level – Physical data model.
- Relational or Representational
- Object-oriented Data Models:
- Object-Relational Models:
- High Level-conceptual data model: User level data model is the high level or conceptual model. This provides concepts that are close to the way that many users perceive data.
2 .Low level-Physical data model : provides concepts that describe the details of how data is stored in the computer model. Low level data model is only for Computer specialists not for end-user.
- Representation data model: It is between High level & Low level data model
Which provides concepts that may be understood by end-user but that are not too far removed from the way data is organized by within the computer.
The most common data models are
1. Relational Model
The Relational Model uses a collection of tables both data and the relationship among those data. Each table have multiple column and each column has a unique name. Relational database comprising of two tables Customer –Table.
Customer-Name Security Number
Address City Account- Number Preethi 111-222-3456 Yelhanka Bangalore A- Sharan 111-222-3457 Hebbal Bangalore A- Preethi 112-123-9878 Jaynagar Bangalore A- Arun 123-987-9909 MG road Bangalore A- Preethi 111-222-3456 Yelhanka Bangalore A- Rocky 222-232-0987 Sanjay Nagar Bangalore A- Account –Table Account-Number Balance A-101 1000. A-125 1200. A-456 5000. A-987 1234. A-111 3000. Customer Preethi and Rocky share the same account number A- Advantages
- The main advantage of this model is its ability to represent data in a simplified format.
- The process of manipulating record is simplified with the use of certain key attributes used to retrieve data.
- Representation of different types of relationship is possible with this model. 2. Network Model
The data in the network model are represented by collection of records and relationships among data are represented by links, which can be viewed as pointers. Preethi 111-222-3456 yelhanka Bangalore
A-101 1000.
A-111 3000.
