database management system (dbms) lecture notes | advantages | type

Read lecture notes of database management system (dbms) and from below you will get its advantage, type and component. Database management as we are all aware, is critical for transaction processing. However, during the initial period of computer applications to the computer, the data was maintained/stored depending upon its use for the application. Under this approach, each user system had its master files and transaction files, which were processed separately. Although the data required by many systems were standard, there used to be the repetition of data stored in various user systems, leading to data redundancy.

Read more about information security and control and information system quality

The data redundancy, in turn, resulted in complexities in data management as all data has to be identical and currently updated in all the files, simultaneously. Data redundancy also resulted in lack of integrity and inconsistency of data available/stored in various user files. The database approach emerged out of the need, indeed urgency, to eliminate the data management problems. The database is pivotal to MIS. A data bank could be defined as “A mechanical/automated, formally defined, the centrally controlled collection of data in an organization.” The database implies a particular structuring of data, both conceptual/ logical and physical. Instead of storing the data separately in different locations/ files for various applications, the data records are physically organized and stored, so as to promote data sharing, availability, data consistency, security, and integrity, which are the primary objectives of the database approach.

Database management system

The Database Management System (DBMS), as it is popularly known, acts as the interface between the application programs and the data. DBMS is a software system which performs the functions of defining, creating, revising and controlling the database. DBMS is a specially designed software to creating and maintaining a database and enable individual business applications to extract the data they need without having to build separate files in their computer programs. A DBMS is a software that provides services for accessing a database, while maintaining all the essential features of the data.

Database Instances and Schemas

Database changes as information is inserted and deleted. The collection of information stored in the database at a particular moment is called as an instance of the database. The overall design of the database is called the database schema.

Characteristics of Data in DBMS

1. Data sharing: Data should be shared amongst different users and applications
2. Data Independence: Changes made in the schema at one level should not affect other levels.
3. Controlled redundancy: Data is not duplicated, however, any duplication is deliberate and controlled.
4. Validity/Integrity/Correctness: Data entered should be correct concerning the real world entity that they represent.
5. Security: Data should be protected from unauthorized users.

Advantages of DBMS

The following can be said to be the primary benefits of the DBMS:

1. The DBMS helps reduce the complexity in the systems’ environment due to the central control/management of data, access, utilization, and security.
2. As same data elements are not repeated in all the files, DBMS helps reduce/eliminate data redundancy and inconsistency and promotes data integrity throughout the system/organization.
3. The DBMS provides for central control of data creation and definition, thereby reducing/eliminating data confusion.
4. DBMS helps bring about the substantial reduction in the costs related to program development and maintenance.
5. DBMS supports separate logical view and physical arrangement, thereby, reducing program-data dependence.
6. DBMS, particularly the RDBMS, permits ad-hoc queries, thus ensuring flexibility of information systems.
7. DBMS helps increase access and availability of information.

Database Languages

The database provides two different types of languages: one to specify the database schema and the other to express database queries and updates.

1. Data Definition Language (DDL): DDL is the formal language used by the computer professionals to specify the database schema. The result of compilation of DDL statements is a set of tables. It defines each data element as it appears in the database. The data element is then translated into the format desired/required by the application’s program.

2. Data Manipulation Language (DML): It is a specialized language, which is used by the end-users and programmers to manipulate data in the database. By data manipulation we mean:
a. The retrieval of information stored
b. The insertion of new data
c. The deletion of data
d. The modification of information stored

DML consists of commands, which enable end-users and programmers to extract data from the database to satisfy information requests and develop applications.

DMLs are mainly of two types:

i. Procedural DML: It requires the user to specify what data are needed and how to get those data.

ii. Non-procedural DML: It requires the user to specify what data are needed without specifying how to get those data. The Structured Query Language (SQL) is presently the most prominent and popular database language used. A query is a statement requesting the retrieval of information. The portion of a DML that involves information retrieval is called as the query language.

DBMS components

The major components of DBMS are

1. Transaction management: A transaction is a sequence of database operations that represents a logical unit of work and that accesses a database and transforms it from one state to another. A transaction can update, delete or modify a single or a set of records. When the DBMS does a “commit” the changes made by the transaction are made permanent to the database. If the changes are not to be made permanent, the transaction can be rolled back, and the database will remain in its original state.

2. Concurrency control: Concurrency control is the database management activity of coordinating the actions of database manipulation process that operate concurrently; that access shared data and can potentially interfere with one another. The goal of an ideal concurrency management mechanism is to allow concurrency while maintaining the consistency of the shared data.

3. Recovery management: It ensures that aborted or failed transactions do not create an adverse effect on the database or other operations. It also ensures that the database is returned to a consistent state after an operation fails or aborts. Recovery is related to concurrency — more the concurrency, the more is the chance that an aborted transaction can affect many other operations.

4. Security management: It refers to the protection of data against unauthorized access only authorized users are given access to the data in the database. The level of access for each user and the type of operation the user can perform on data will depend on the access privileges of the users.

5. Language interface: It provides support languages used for the definition and manipulation of the data in the database.

6. Storage management: The DBMS provides a mechanism for management of permanent storage of the data. The internal schema defines how the data should be stored by the storage management device and the storage manager interfaces with the operating system to access the physical storage.

7. Data catalog management: Data directory also called data dictionary is a system database that contains the description of the information in the database (metadata). It provides information about data, relationships, constraints and the entire schema that organize these features into a unified database. The data catalog can be queried to get information about the structure of the database.

DATABASE MODEL

There are three types of database models commonly in use in business organizations. These models are used for keeping track of entities, attributes, and relationships. The three database types are

1. Hierarchical Database Model (HDBM): The Hierarchical Database Model is one of earliest DBMS, when the computer applications focused on processing large data like sales order processing, check processing, inventory updating, etc. This Model follows a structured organizational mode. It represents information in a pyramidal or tree-like structure. Each record appears to be like an organizational chart with one top- level segment, called the root, spreading downwards into branches and leaves.

Under this Model, there is a record. Within each record, data elements are organized into pieces of the document called segments. An upper segment is connected logically to a lower part of a parent-child relationship. A parent section can have more than one child, but a child can have only one parent, indicating a one-to-many relationship. The Hierarchical Model is, thus, highly structured and requires a controlled, finite and rule-based approach, where record and its segments are connected to each other in one-to-many parent-child relationships. The most common hierarchical DBMS has been the Information Management System (IMS) released by the IBM in 1968.

2. Network Database Model (NDBM): The NDBM is a variation of the earlier Hierarchical Database Model. The Network Model features data logically as the many-to-many relationship. To put it more succinctly, just as “parents can have multiple children,” a “child” too can have more than one “parent.” The many-to-many relationship under this Model. It would be observed that the data regarding the salesperson could be made use of/for:

i. Understanding/analyzing “Sales Zone” performance.
ii. Analyzing sales/recovery position.
iii. Analyzing product-wise sales performance.

The US giant business corporation General Electric used the Network Model during the mid-60s, and their model was known as the Integrated Data Store (IDS). GE under the leadership of Charles Bachman developed the model. The model used blocks, area, and arrows to represent the organization’s database. This method is popularly known as “Bachman’s Diagram.” IDS, it may be noted, emerged to be the standard of the CODASYL Group, an organization of major hardware and software vendors.

3. Relational Database Model (RDBM): The Relational Database Model is the most recent of the three database models and was proposed by Dr. E. F. Codd in 1970. The Model represents all data in the database as simple two-dimensional tables called “Relations.” The table has rows and columns, the rows representing individual records and the columns representing attributes of each file. Although the tables appear to be similar to flat files, the information in more than one file can be easily extracted and combined to suit the user’s specific requirements, thereby providing ad-hoc request flexibility/facility. The key is the separation of the data on logical and physical levels, which is made possible by the use of sophisticated mathematical algorithms and notations, which are utilized in the relational model.

4. Other Data Models: The other data models include the Object-Oriented Data Model that has been used widely in the Relational Model. It includes the concept of encapsulation, methods and object identity.

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