Components of the Database System Environment

Components of the Database System Environment

There are five major components in the database system environment and their interrelationship are.

• Hardware

• Software

• Data

• Users

• Procedures

                      

1.Hardware: The hardware is the actual computer system used for keeping and accessing the database. Conventional DBMS hardware consists of secondary storage devices, usually hard disks, on which the database physically resides, together with the associated Input-Output devices, device controllers and· so forth. Databases run on a' range of machines, from Microcomputers to large mainframes. Other hardware issues for a DBMS includes database machines, which is hardware designed specifically to support a database system.

2. Software: The software is the actual DBMS. Between the physical database itself (i.e. the data as actually stored) and the users of the system is a layer of software, usually called the Database Management System or DBMS. All requests from users for access to the database are handled by the DBMS. One general function provided by the DBMS is thus the shielding of database users from complex hardware-level detail.

The DBMS allows the users to communicate with the database. In a sense, it is the mediator between the database and the users. The DBMS controls the access and helps to maintain the consistency of the data. Utilities are usually included as part of the DBMS. Some of the most common utilities are report writers and application development.

                         

3. Data : It is the most important component of DBMS environment from the end users point of view. As shown in observes that data acts as a bridge between the machine components and the user components. The database contains the operational data and the meta-data, the 'data about data'.

The database should contain all the data needed by the organization. One of the major features of databases is that the actual data are separated from the programs that use the data. A database should always be designed, built and populated for a particular audience and for a specific purpose.

4. Users : There are a number of users who can access or retrieve data on demand using the applications and interfaces provided by the DBMS. Each type of user needs different software capabilities. The users of a database system can be classified in the following groups, depending on their degrees of expertise or the mode of their interactions with the DBMS. The users can be:

• Naive Users

• Online Users

• Application Programmers

• Sophisticated Users

• Data Base Administrator (DBA)

Naive Users: Naive Users are those users who need not be aware of the presence of the database system or any other system supporting their usage. Naive users are end users of the database who work through a menu driven application program, where the type and range of response is always indicated to the user.

A user of an Automatic Teller Machine (ATM) falls in this category. The user is instructed through each step of a transaction. He or she then responds by pressing a coded key or entering a numeric value. The operations that can be performed by valve users are very limited and affect only a precise portion of the database. For example, in the case of the user of the Automatic Teller Machine, user's action affects only one or more of his/her own accounts.

Online Users : Online users are those who may communicate with the database directly via an online terminal or indirectly via a user interface and application program. These users are aware of the presence of the database system and may have acquired a certain amount of expertise with in the limited interaction permitted with a database.

Sophisticated Users : Such users interact with the system without ,writing programs.

Instead, they form their requests in database query language. Each such query is submitted to a very processor whose function is to breakdown DML statement into instructions that the storage manager understands.

Specialized Users : Such users are those ,who write specialized database application that do not fit into the fractional data-processing framework. For example: Computer-aided design systems, knowledge base and expert system, systems that store data with complex data types (for example, graphics data and audio data).

Application Programmers : Professional programmers are those who are responsible for developing application programs or user interface. The application programs could be written using general purpose programming language or the commands available to manipulate a database.

Database Administrator: The database administrator (DBA) is the person or group in charge for implementing the database system ,within an organization. The "DBA has all the system privileges allowed by the DBMS and can assign (grant) and remove (revoke) levels of access (privileges) to and from other users. DBA is also responsible for the evaluation, selection and implementation of DBMS package. 

5. Procedures: Procedures refer to the instructions and rules that govern the design and use of the database. The users of the system and the staff that manage the database require documented procedures on how to use or run the system.

These may consist of instructions on how to:

• Log on to the DBMS.

• Use a particular DBMS facility or application program.

• Start and stop the DBMS.

• Make backup copies of the database.

• Handle hardware or software failures.

Change the structure of a table, reorganize the database across multiple disks, improve performance, or archive data to secondary storage.

Advantage and Disadvantage of DDBMS

A DDBMS (distributed database management system) is a centralized application that manages a single logical database   as if it were all stored on the same computer. The DDBMS synchronizes all the data periodically, and in cases where multiple users must access the same data, ensures that updates and deletes performed on the data at one location will be automatically reflected in the data stored elsewhere.

The distribution of data and applications has potential advantages over traditional centralized database systems. Unfortunately, there are also disadvantages; in this section we review the advantages and disadvantages of DDBMS.

Advantages

There are following advantages of DDBMs:

Reflects organizational structure Many organizations are naturally distributed over several locations. For example, a bank has many offices in different cities. It is natural for databases used in such an application to be distributed over these locations. A bank may keep a database at each branch office containing details such things as the staff that work at that location, the account information of customers etc.

The staff at a branch office will make local inquiries of the database. The company headquarters may wish to make global inquiries involving the access of data at all or a number of branches.

Improved share ability and local autonomy The geographical distribution of an organization can be reflected in the distribution of the data; users at one site can access data stored at other sites. Data can be placed at the site close to the users who normally use that data. In this way, users have local control of the data, and they can consequently establish and enforce local policies regarding the use of this data. A global database administrator (DBA) is responsible for the entire system. Generally, part of this responsibility is assigned the local level, so that the local DBA can manage the local DBMS.

Improved availability In a centralized DBMS, a computer failure terminates the applications of the DBMS. However, a failure at one site of a DDBMS, or a failure of a communication link making\ some sites inaccessible, does not make the entire system in opera bite. Distributed DBMSs are designed to continue to function despite such failures. If a single node fails, the system may be able to reroute the failed node's requests to another site.

Improved reliability

As data may be replicated so that it exists at more than one site, the failure of a node or a communication link does not necessarily make the data inaccessible.

Improved Performance As the data is located near the site of 'greatest demand', and given the inherent parallelism of distributed DBMSs, speed of database access may be better than that achievable from a remote centralized database. Furthermore, since each site handles only a part of the entire database, there may not be the same contention for CPU and I/O services as characterized by a centralized DBMS.

Economics

It is now generally accepted that it costs much less to create a system of smaller computers with the equivalent power of a single large computer. This makes it more cost effective for corporate divisions and departments to obtain separate computers. It is also much more cost-effective to add workstations· to a network than to update a mainframe system.

The second potential cost saving occurs where database are geographically remote and the applications require access to distributed data. In such cases, owing to the relative expense of data being transmitted across the network as opposed to the cost of local access, it may be much more economical to partition the application and perform the processing locally at each site.

Modular growth

In a distributed environment, it is much easier to handle expansion. New sites can be added to the network without affecting the operations of other sites. This flexibility allows an organization to expand relatively easily. Adding processing and storage power to the network can usually handle the increase in database size. In a centralized DBMS, growth may entail changes to both hardware (the procurement of a more powerful system) and software (the procurement of a more powerful or more configurable DBMS).

Disadvantages of DDBMS

There are following disadvantages of DDBMSs:

Complexity

A distributed DBMS that hides the distributed nature from the user and provides an acceptable level of performance, reliability, availability is inherently more complex then a centralized DBMS. The fact that data can be replicated also adds an extra level of complexity to the distributed DBMS. If the software does not handle data replication adequately, there wi1l be degradation in availability, reliability and performance compared with the centralized system, and the advantages we cites above will become disadvantages.

Cost

Increased complexity means that we can expect the procurement and maintenance costs for a DDBMS to be higher than those for a centralized DBMS. Furthermore, a distributed

DBMS requires additional hardware to establish a network between sites. There are ongoing communication costs incurred with the use of this network. There are also additional labor costs to manage and maintain the local DBMSs and the underlying network.

Security

In a centralized system, access to the data can be easily controlled. However, in a distributed DBMS not only does access to replicated data have to be controlled in multiple locations but also the network itself has to be made secure. In the past, networks were regarded as an insecure communication medium. Although this is still partially true, significant developments have been made to make networks more secure.

Integrity control more difficult

Database integrity refers to the validity and consistency of stored data. Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate. Enforcing integrity constraints generally requires access to a large amount of data that defines the constraints. In a distributed DBMS, the communication and processing costs that are required to enforce integrity constraints are high as compared to centralized system.

Lack of Standards

Although distributed DBMSs depend on effective communication, we are only now starting to see the appearance of standard communication and data access protocols. This lack of standards has significantly limited the potential of distributed DBMSs. There are also no tools or methodologies to help users convert a centralized DBMS into a distributed DBMS

Lack of experience

General-purpose distributed DBMSs have not been widely accepted, although many of the protocols and problems are well understood. Consequently, we do not yet have the same level of experience in industry as we have with centralized DBMSs. For a prospective adopter of this technology, this may be a significant deterrent.

Database design more complex

Besides the normal difficulties of designing a centralized database, the design of a distributed database has to take account of fragmentation of data, allocation of fragmentation to specific sites, and data replication

Function of RDBMS

Few Important Functions are as follow:

1. Data Dictionary Management:

Data Dictionary is where the DBMS stores definitions of the data elements and their relationships (metadata). The DBMS uses this function to look up the required data component structures and relationships. When programs access data in a database they are basically going through the DBMS. This function removes structural and data dependency and provides the user with data abstraction. In turn, this makes things a lot easier on the end user. The Data Dictionary is often hidden from the user and is used by Database Administrators and Programmers.

2. Data Storage Management:

This particular function is used for the storage of data and any related data entry forms or screen definitions, report definitions, data validation rules, procedural code, and structures that can handle video and picture formats. Users do not need to know how data is stored or manipulated. Also involved with this structure is a term called performance tuning that relates to a database’s efficiency in relation to storage and access speed.

3. Data Transformation and Presentation:

This function exists to transform any data entered into required data structures. By using the data transformation and presentation function the DBMS can determine the difference between logical and physical data formats.

4. Security Management:

This is one of the most important functions in the DBMS. Security management sets rules that determine specific users that are allowed to access the database. Users are given a username and password or sometimes through biometric authentication (such as a fingerprint or retina scan) but these types of authentication tend to be more costly. This function also sets restraints on what specific data any user can see or manage.

5. Multiuser Access Control:

Data integrity and data consistency are the basis of this function. Multiuser access control is a very useful tool in a DBMS, it enables multiple users to access the database simultaneously without affecting the integrity of the database.

6. Backup and Recovery Management:

Backup and recovery is brought to mind whenever there is potential outside threats to a database. For example if there is a power outage, recovery management is how long it takes to recover the database after the outage. Backup management refers to the data safety and integrity; for example backing up all your mp3 files on a disk.

7. Data Integrity Management:

The DBMS enforces these rules to reduce things such as data redundancy, which is when data is stored in more than one place unnecessarily, and maximizing data consistency, making sure database is returning correct/same answer each time for same question asked.

8. Database Access Languages and Application Programming Interfaces:

A query language is a nonprocedural language. An example of this is SQL (structured query language). SQL is the most common query language supported by the majority of DBMS vendors. The use of this language makes it easy for user to specify what they want done without the headache of explaining how to specifically do it.

9. Database Communication Interfaces:

This refers to how a DBMS can accept different end user requests through different network environments. An example of this can be easily related to the internet. A DBMS can provide access to the database using the Internet through Web Browsers (Mozilla Firefox, Internet Explorer, Netscape).

10. Transaction Management:

This refers to how a DBMS must supply a method that will guarantee that all the updates in a given transaction are made or not made. All transactions must follow what is called the ACID properties.

A – Atomicity: states a transaction is an indivisible unit that is either performed as a whole and not by its parts, or not performed at all. It is the responsibility of recovery management to make sure this takes place.

C – Consistency: A transaction must alter the database from one constant state to another constant state.

I – Isolation: Transactions must be executed independently of one another. Part of a transaction in progress should not be able to be seen by another transaction.

D – Durability: A successfully completed transaction is recorded permanently in the database and must not be lost due to failures.