Oracle Database

Oak Ridge Automatic Computer and Logical Engine

Regards,

Manikandan Selvarajan

dB Professionals India Pvt Ltd,

Chennai-40,

India.

Advantages:

• It allows for better quality data, as you restrict what data goes into a column or a table.
• It allows for data to be linked between tables, using foreign key constraints

Disadvantages:

• Takes a little longer to set up a table as the constraints need to be identified and added into the script.

DBMS Interfaces

User-friendly interfaces provided by a DBMS may include the following. � Menu-Based interfaces for Web Clients or Browsing: These interfaces present user with lists of options, called menus, that lead the user through the formulation a request. Menus do away with the need to memorize the specific commands and syntax of a query language. Pull-down menus are a very popular technique in Web based user interfaces. They are also often used in browsing interfaces, which allows a user to look through the contents of a database. � Forms-Based Interfaces: A forms-based interface displays a form to each user. Forms are usually designed and programmed for naive users as interfaces to canned transactions. Some systems have utilities that define a form by letting the end user interactively construct a sample form on the screen. � Graphical User Interfaces: A graphical interface (GUI) typically displays a schema to the user in diagrammatic form. The user can then specify a query by manipulating diagram. In many cases, GUls utilize both menus and forms. Most GUls use a pointing device, such as a mouse, to pick certain parts of the displayed schema diagram. � Natural Language Interfaces: These interfaces accept requests written in English, Hindi or some other language and attempt to "understand" them. A natural language interface usually has its own "schema," which is similar to the database conceptual schema, as well as a dictionary of important words. � Interfaces for Parametric Users: Parametric users, such as bank tellers, often have a small set of operations that they must perform repeatedly. Systems analysts and programmers design and implement a special interface for each known class of na�ve users. Usually, a small set of abbreviated commands is included, with the goal of minimizing the number of keystrokes required for each request. For example, function keys in a terminal can be programmed to initiate the various commands. � Interfaces for the DBA. Most database systems contain privileged commands that can be used only by the DBA's staff. These include commands for creating account, setting system parameters, granting account authorization, changing a schema, and reorganizing the storage structures of a database.

Answer:

Oracle is a data base

Hope this helps!

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We now discuss a conceptual framework for a DBMS. Several different frameworks have been suggested over the last several years. For example, a framework may be developed based on the functions that the various components of a DBMS must provide to its users. It may also be based on different views of data that are possible within a DBMS. We consider the latter approach.

A commonly used views of data approach is the three-level architecture suggested by ANSI/SPARC (American National Standards Institute/Standards Planning and Requirements Committee). ANSI/SPARC produced an interim report in 1972 followed by a final report in 1977. The reports proposed an architectural framework for databases. Under this approach, a database is considered as containing data about an enterprise. The three levels of the architecture are three different views of the data:

1. External - individual user view
2. Conceptual - community user view
3. Internal - physical or storage view

The three level database architecture allows a clear separation of the information meaning (conceptual view) from the external data representation and from the physical data structure layout. A database system that is able to separate the three different views of data is likely to be flexible and adaptable. This flexibility and adaptability is data independence that we have discussed earlier.

We now briefly discuss the three different views.

The external level is the view that the individual user of the database has. This view is often a restricted view of the database and the same database may provide a number of different views for different classes of users. In general, the end users and even the applications programmers are only interested in a subset of the database. For example, a department head may only be interested in the departmental finances and student enrolments but not the library information. The librarian would not be expected to have any interest in the information about academic staff. The payroll office would have no interest in student enrolments.

The conceptual view is the information model of the enterprise and contains the view of the whole enterprise without any concern for the physical implemenation. This view is normally more stable than the other two views. In a database, it may be desirable to change the internal view to improve performance while there has been no change in the 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:

1. Storage allocation e.g. B-trees, hashing etc.
2. Access paths e.g. specification of primary and secondary keys, indexes and pointers and sequencing.
3. Miscellaneous e.g. data compression and encryption techniques, optimisation 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:

1. Staff number, name and address.
2. Staff tax information e.g. number of dependents.
3. Staff bank information where salary is deposited.
4. 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 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.