1. There is the problem with the conventional file systems. In early days, the database applications were made on the top of the file system. There are many drawbacks of using file systems:
1. Redundancy in data and inconsistency: it means there are many file formats and duplicate information exists in the different files.
2. The access to data id difficult: for creating the new task, there is the requirement to write the new program.
3. Data isolation: there should be multiple files and the formats. This is difficult to separate the files from one another.
4. Problems in integrity: there is problem to add the new constraint or change the existing constraints in the files.
5. Atomicity: there should be failure due to the electricity problem or any other problem which will lead to inconsistent data.
6. Concurrent access by the multiple users: there is no controlled concurrent access to the files.
7. Security problems
Database provides the solution to all others problems that are occurred in the file system. Database provides the consistent data. There no problem of atomicity. The data isolation is easily by the database. Database should also provides the security to the data. So database is necessary. (siber schartz)
2. An entity is the object with the physical existence that is specific person, car, and employee. Or it is the object with the conceptual existence. For example, to develop the database for the college to maintain the information of the students, the application should be capable to store and give the data on student such as when the student is admitted; is the student still studied in the college, if the student left then when did he should be left the college; in which department student would be studied. In this example, the entities are college, department, and student.
Attributes: an attribute is the property that depicts the entity. In the above example, the student is the entity and the student’s name, age, address and course are the attributes. ( Unit 2: Entities and Attributes )
3. Business rules is the statement that describes or constrains the aspects of the business. This is intended to declare the structure of the business or to control the behavior of the business. Te business rules are atomic in nature and they are not classified further in any category. There are mainly 3 rues that are affecting the business. A great example of the business rule is marriage. For many business organizations, the manager is would not permit to marry an employee at the company is not permit to marry another accountant. Business rules are used every time to describe the entities, attributes and the relationships and constraints. These rules help the employees to aim at and implement the actions inside the organization environment. (Database Management business rule)
4. A conceptual model invent that there is the want to store the information about every person in the organization. A conceptual model might involve the some of the significant attributes to supplement the definition and revelation of the entities. There is no need of effort for the inventory the full attribute population of the model. It should have the some recognizing concepts but it does not involve the full scheme of recognition.
The physical model of database is the singe logical model instantiated in the particular product of database management in the particular installation. The physical data model states the implementation details which might be the features of the specific product as well as the arrangement choices for that database. This will involve the construction of the index, declarations of the alternate key, constraints and the physical storage. (Science, 1997)
References:
Unit 2: Entities and Attributes . (n.d.). Retrieved from www.nrtechnology.com: http://www.nrtechnology.com/education/database/lecture%202/lecture%202.htm
Database Management business rule. (n.d.). Retrieved from databasemanagement.wikia.com: http://databasemanagement.wikia.com/wiki/Business_Rules
Science, A. I. (1997). Conceptual, Logical ,physical models. Retrieved from www.aisintl.com: http://www.aisintl.com/case/CDM-PDM.html
siber schartz, k. a. (n.d.). Database system concept. Retrieved from homepages.cwi.nl: http://homepages.cwi.nl/~manegold/teaching/DBtech/slides/ch1-8.pdf

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