Relational Database Management Systems


A relational database management system (RDBMS) is a program that lets you create, update, and administer a relational database. Most commercial RDBMS's use the Structured Query Language (SQL) to access the database, although SQL was invented after the development of the relational model and is not necessary for its use. 

The leading RDBMS products are Oracle, IBM's DB2 and Microsoft's SQL Server. Despite repeated challenges by competing technologies, as well as the claim by some experts that no current RDBMS has fully implemented relational principles, the majority of new corporate databases are still being created and managed with an RDBMS.

 RDBs organize data in different ways. Each table is known as a relation, which contains one or more data category columns. Each table record (or row) contains a unique data instance defined for a corresponding column category. 

One or more data or record characteristics relate to one or many records to form functional dependencies. These are classified as follows:
·        One to One: One table record relates to another record in another table.
·        One to Many: One table record relates to many records in another table.
·        Many to One: More than one table record relates to another table record.
·        Many to Many: More than one table record relates to more than one record in another table.
RDB performs "select", "project" and "join" database operations, where select is used for data retrieval, project identifies data attributes, and join combines relations.

RDBs have many other advantages, including:
·        Easy extendability, as new data may be added without modifying existing records. This is also known as scalability.
·        New technology performance, power and flexibility with multiple data requirement capabilities.
·        Data security, which is critical when data sharing is based on privacy. For example, management may share certain data privileges and access and block employees from other data, such as confidential salary or benefit information.

Object-oriented Database Management Systems.

In database management systems. it divided into four type. That is hierarchical database, relational database, networks database and object-oriented. In this article I would like to give a simple briefing about the database management systems. here I will give a full explanation about the object-oriented programming. Object-oriented databases is an object database (also object-oriented database management system) is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are table-oriented. Object-relational databases are a hybrid of both approaches. It also able to handle many new data types, including graphics, photographs, audio, and video. Then, use small, reusable chunks of software called objects. Each object consists of two elements. First, a piece of data. Example, sound, video, text, or graphics. Second, the instructions, or software programs called methods. In this database management systems, the advantages of the object-oriented database is a ability to mix and match reusable objects provides incredible multimedia capability. Besides, it designer can specify the structure of objects and their behavior (methods). Next advantages is better interaction with object-oriented languages such as Java and C++. Then, it is less code required when applications are object oriented and easier navigation. It also data model  is based on the real world. Lastly, it reduced maintenance. The primary goal of object-oriented development is the assurance that the system will enjoy a longer life while having far smaller maintenance costs.  Because most of the processes within the system are encapsulated, the behaviours may be reused and incorporated into new behaviours. And the disadvantages of the object-oriented databases is more costly to develop. Besides, it reluctant to abandon or convert from existing database that they have spent for. Next advantages  is lower efficiency when data is simple and relationships are simple. Then, it lesser user tools compared to Relational DBMS. Lastly, it less stable. 

The Hierarchical Database System

In database management system, there is divided into four type that is hierarchical database, network database, relational database and object-oriented database. Each database system has difference than each of the type. And each database system have each benefit and some lacking towards each others. The most useful and quite popular use is hierarchical database.  The hierarchical database is a model which 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 also 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, like set theory used in the relational model, "borrowed" from maths. For example, an organization might store information about an employee, such as name, employee number, department, salary. The organization might also store information about an employee's children, such as name and date of birth. The employee and children data forms a hierarchy, where the employee data represents the parent segment and the children data represents the child segment. If an employee has three children, then there would be three child segments associated with one employee segment. In a hierarchical database the parent-child relationship is one to many. This restricts a child segment to having only one parent segment. There is some advantages in this hierarchical database. The advantages of hierarchical database is firstly simplicity. Its  mean,  the database is based on the hierarchical structure and the relationship between the various layers is logically simple. Secondly is data security. Hierarchical model was the first database model that offered the data security that is provided by the DBMS. Next, the advantages of hierarchical database is a data integrity. It  is based on the parent child relationship and  there is always a link between the parent segment and the child segment under it. Lastly is a efficiency. It is a very efficient when the database contains a large number of 1:N  relationship and when the user require large number of transaction. and also there is some disadvantage in this database systems. The disadvantages of  hierarchical database is each child only have one parent. Beside, linkage between children are not allowed. Next, implementation complexity. Although  it is simple and easy to design, it is quite complex to implement. Then, database  management problem. If you make any changes in the database structure, then you need to make changes in the entire application program that access the database. Lack of structural independence also is a disadvantages of  hierarchical database. There is a lack of structural independence because when we change the structure then it becomes compulsory to change the application too. Lastly,  operational anomalies. Its mean, hierarchical model suffers from the insert, delete and update anomalies and also retrieval operation is difficult. This is only about the hierarchical database systems. This type of database is quite useful for some organization because it really user-friendly and give many benefits.