Some well known RDMS:
4th Dimension
Adaptive Server Enterprise
Apache Derby
MS SQL Server
HP NonStop SQL
Oracle Rdb
OpenLink Virtuoso
Pervasive PSQL
Pyrrho DBMS
SQL Anywhere

Databases have been in use since the earliest days of electronic computing. Unlike modern systems which can be applied to widely different databases and needs, the vast majority of older systems were tightly linked to the custom databases in order to gain speed at the expense of flexibility. Originally DBMSs were found only in large organizations with the computer hardware needed to support large data sets. more

Database Management Systems

Definition: A Database Management System (DBMS) is a collection of software programs which enable large, structured sets of data to be stored, modified, extracted and manipulated in different ways.

Features: Database Management Systems have often been characterized as “Attribute Management Systems”. Attributes are pieces of information (with unique values) that describe an object (for e.g. size, color, and shape) and combine many of the services necessary for advanced attribute management without the need for a variety of different programs.

Database Management Systems employ the use of a query language and report writers to interrogate the database and analyze its data. Queries allow users to search, sort, and analyze specific data by granting users efficient access to the required information. For example, one would use a query command to make the system retrieve data regarding all articles of clothing which come in the color blue. The most common query language used to access database systems is the Structured Query Language (SQL).

The DBMS also provides security features that protect against unauthorized users trying to gain access to confidential database information; and prevent data loss in case of a system crash. Depending on the settings, users are allowed access to either all, or specific database subschemas, through the use of passwords. For example, while a database may contain detailed customer information, certain users may only be allowed access to customer names and addresses, while others may be able to view payment specifications. Access and change logs can be programmed to add even more security to a database, recording the date, time and details of any user making any alteration to the database. Furthermore, the DBMS is also responsible for the database’s integrity, ensuring that no two users are able to update the same record at the same time, as well as preventing duplicate entries, such as two employees being given the same employee number.

Database Models: Database information normally consists of subjects, such as customers, employees or suppliers; as well as activities such as orders, payments or purchases. This information must be organized into related record types through a process known as database design. The DBMS that is chosen must be able to manage different relationships, which is where database models come in.

Hierarchical databases organize data under the premise of a basic parent/child relationship. Each parent can have many children, but each child can only have one parent. In hierarchical databases, attributes of specific records are listed under an entity type and entity types are connected to each other through one-to-many relationships, also known as 1:N mapping. Originally, hierarchical relationships were most commonly used in mainframe systems, but with the advent of increasingly complex relationship systems, they have now become too restrictive and are thus rarely used in modern databases. If any of the one-to-many relationships are compromised, for e.g. an employee having more than one manager, the database structure switches from hierarchical to a network.

In the network model of a database it is possible for a record to have multiple parents, making the system more flexible compared to the strict single-parent model of the hierarchical database. The model is made to accommodate many to many relationships, which allows for a more realistic representation of the relationships between entities. Even though the network database model enjoyed popularity for a short while, it never really lifted of the ground in terms of staging a revolution. It is now rarely used because of the availability of more competitive models that boast the higher flexibility demanded in today’s ever advancing age.

Relational databases (RDBMS) are entirely unique when compared to the aforementioned models as the design of the records is organized around a set of tables (with unique identifiers) to represent both the data and their relationships. The fields to be used for matching are often indexed in order to speed up the process and the data can be retrieved and manipulated in a number of ways without the need to reorganize the original database tables. Working under the assumption that file systems (which often use the hierarchical or network models) are not considered databases, the relational database model is the most commonly used system today. While the concepts behind hierarchical and network database models are older than that of the relational model, the latter was in fact the first one to be formally defined.

After the relational DBMS soared to popularity, the most recent development in DMBS technology came in the form of the object-oriented database model, which offers more flexibility than the hierarchical, network and relational models put together. Under this model, data exists in the form of objects, which include both the data and the data’s behavior. Certain modern information systems contain such convoluted combinations of information that traditional data models (including the RDBMS) remain too restrictive to adequately model this complex data. The object-oriented model also exhibits better cohesion and coupling than prior models, resulting in a database which is not only more flexible and more manageable but also the most able when it comes to modeling real-life processes. However, due to the immaturity of this model, certain problems are bound to arise, some major ones being the lack of an SQL equivalent as well as lack of standardization. Furthermore, the most common use of the object oriented model is to have an object point to the child or parent OID (object I.D.) to be retrieved; leaving many programmers with the impression that the object oriented model is simply a reincarnation of the network model at best. That is, however, an attempt at the over-simplification of an innovative technology.

Database Management System Software: There are innumerable numbers of DBMS software available in the market. Some of the most popular ones include Oracle, IBM’s DB2, Microsoft Access, Microsoft SQL Server, MySQL and FileMaker. MySQL, one of the most popular database management systems used by online entrepreneurs is one example of an object-oriented DBMS. Microsoft Access (another popular DBMS) on the other hand is not a fully object oriented system, even though it does flaunt certain aspects of it.