(Homework Solution): Question 1 Define a database system.[5 marks] b. a. Within the context of database systems,

Question 1:

a.)

Ans: A database is simply an organized collection of related data, typically stored on disk or any storage medium that can be used remotely or directly, and accessible by possibly many concurrent users. Databases are generally separated into application areas. For example, one database may contain Human Resource (employee and payroll) data; another may contain sales data; another may contain accounting data; and so on.

To mantail the databese system, we need a database managemant system(DBMS). DBMS is a set of programs that manages any number of databases.

A DBMS is responsible for:

• Data Independence.
• Data Reduncancy.
• Data Integrity.
• Data Security.

etc.

b.)

Ans:

i)    Data Independence

A database system normally contains a lot of data in addition to users’ data. For example, it stores data about data, known as metadata, to locate and retrieve data easily. It is rather difficult to modify or update a set of metadata once it is stored in the database. But as a DBMS expands, it needs to change over time to satisfy the requirements of the users. If the entire data is dependent, it would become a tedious and highly complex job. Data itself follows a layered architecture, so that when we change data at one layer, it does not affect the data at another level. This data is independent but mapped to each other.

There are two types of data independency

• Logical independence
• Physical Independence

ii)    Data Redundency

Data redundancy is the repetition or superfluity of data. Data redundancy data is an common issue in computer data storage and database systems. Redundancy in database means that some data fields are repeated in the database.

This data repetition may occur either if a field is repeated in two or more tables or if the field is repeated within the table.Data can appear multiple times in a database for a variety of reasons. For example, a shop may have the same customer’s name appearing several times if that customer has bought several different products at different dates.

iii) Data Intrgrity

Data integrity is the completeness, accuracy and consistency of data. This can be indicated by the absence of alteration between two instances or between two updates of a data record, meaning data is intact and unchanged. Data integrity is usually imposed during the database design phase through the use of standard procedures and rules. Data integrity can be maintained through the use of various error-checking methods and validation procedures.

Data integrity is enforced in both hierarchical and relational database models. The following three integrity constraints are used in a relational database structure to achieve data integrity:

• Entity Integrity: This is concerned with the concept of primary keys. The rule states that every table must have its own primary key and that each has to be unique and not null.
• Referential Integrity: This is the concept of foreign keys. The rule states that the foreign key value can be in two states. The first state is that the foreign key value would refer to a primary key value of another table, or it can be null. Being null could simply mean that there are no relationships, or that the relationship is unknown.
• Domain Integrity: This states that all columns in a relational database are in a defined domain.

iv)    Data Security

Data security is an imperative aspect of database system. It is of particular importance in distributed systems because of large number of users, fragmented and replicated data, multiple sites and distributed control.

• Availability loss: Availability loss refers to non-availability of database objects by legitimate users.
• Integrity loss: Integrity loss occurs when unacceptable operations are performed upon the database either accidentally or any other reason. This may happen while creating, inserting, updating or deleting data. It results in corrupted data leading to incorrect decisions.
• Confidentiality loss: Confidentiality loss occurs due to unauthorized or unintentional disclosure of confidential information. It may result in illegal actions, security threats and loss in public confidenc