Ch1 Introduction to Database Management

Besides redundancy, what other problems are associated with the nondatabase approach to processing data?

- Increased risk of inconsistency - Difficult to obtain information spread across multiple files - Data is not shared among users - Low data integrity - Low amount of security - Programmers waste time writing programs to allow users to access information; decrease productivity - Decreased data independence.

What kinds of responsibilities does a DBA have in a database environment?

- Structure the database in such a way that it benefits the entire organization, not just a single group. - Structure the database to allow users to access information pertinent to their job, i.e. restricting certain groups of users from accessing all parts of the database. - Assign users with passwords to access the database.

What are the advantages of a database?

1) Getting more information from the same amount of data 2) Sharing data 3) Balancing conflicting requirements 4) Controlling redundancy 5) Facilitating consistency 6) Improving integrity 7) Expanding security 8) Increasing productivity 9) Providing data independence

What are the disadvantages of a database?

1) Larger file size 2) Increased complexity 3) Greater impact of failure 4) More difficult recovery

What problems are associated with redundancy?

1) Redundancy wastes space because you're storing data in multiple places, which requires more memory and takes longer to save and open 2) Changing redundant data is time-consuming and tedious as you would need to change it in multiple places 3) It can lead to inconsistencies, such as misspellings

How does a DBMS provide security?

A DBMS can require a password to access data, and even further, it allows for users to be assigned to groups, with certain groups being able to view particular parts of the database. With a non-database approach, there are limited security features.

What is an attribute?

A characteristic or property of an entity

How is a file size a disadvantage in a database environment?

A database would require a large amount of internal memory and disk space due to its ability to hold vast quantities of data.

How do you create a one-to-many relationship in a database system?

A line between entities represents the relationship. The 'one' part of the relationship does not have an arrow on its end of the line, and the 'many' part of the relationship is indicated by a single-headed arrow.

What is an entity?

A person, place, object, event, or idea that is stored

What is a DBMS?

A program or group of programs that allows an individual to interact with a database

What is data independence?

A property that lets you change the structure of the database without requiring you to change the programs that access the database.

What is a database?

A structure that can store information about multiple types of entities, the attributes of those entities, and the relationships between the entities.

What is a relationship?

An association between entities

Why might recovery of data be more difficult in a database environment?

Because of the complex nature of a database, recovery after failure is more complicated than the recovery of a single file. Furthermore, it must be restored to when it was last known to be correct, and any changes done after must be redone. It might get tedious when many people are involved with updating the database.

What is a DBA?

Database Administrator

What is meant by the sharing of data?

Databases allow multiple users to access the same information. For example, if one user edits the address of a customer, all users are able to view this change.

What is an E-R diagram?

Entity-Relationship diagram. A visual way to represent data.

How does consistency result from controlling redundancy?

If a customer's address appears in more than one place, it might be 200 Columbus Dr. in one place and 100 Washington Av. in another. The data is therefore inconsistent. This is a direct result of redundancy, and because a database reduces redundancy, there is less potential for this sort of inconsistency to occur.

If a database is not maintained or if incorrect data is entered into the database, serious problems can occur. What problems could occur if a student database is not maintained?

If a student registers for a class and the database isn't updated, they might show up to that class but not formally enrolled. Additionally, they might enroll for one class, but if the information is incorrectly updated, the system might have them in a different class.

How can you get more information from the same amount of data by using a database approach instead of a nondatabase approach?

In a nondatabase approach, it can be difficult, if not impossible, to obtain the desired information from data spread across several disjointed systems. If the data is stored in a single database, the information becomes available, and obtaining it is quick and easy.

Why can a failure in a database environment be more serious than an error in a nondatabase environment?

In a nondatabase environment, each user has a separate system, so the failure of one system doesn't necessarily affect the others. Conversely, if multiple users are sharing the same database, a failure for one user could affect everyone else.

What is an integrity constraint?

Integrity constraints are used to ensure accuracy and consistency of data in a relational database. Eg. When a new customer is entered, it ensures that the rep and rep number associated with that customer already exists.

What is a form?

Screen objects used to maintain, view, and print data from the database. Forms are used to enter data.

What is redundancy?

The duplication of data or the storing of the same data in more than one place

What is security?

The prevention of unauthorized access to the database

What is a database design?

The structure of the required database

How can the complexity of a DBMS be a disadvantage?

Users of the DBMS must learn a great deal to understand the features of the system in order to take full advantage of it. When constructing the database design, it is possible to make incorrect choices, especially with an insufficient understanding of the system. Small incorrect choices could lead to disaster later on.

When does a database have integrity?

When it satisfies all established integrity constraints

What is a one-to-many relationship?

When one entity is related to multiple other entities

What is a one-to-one relationship?

When one entity is related to only one other entity

An attribute is a characteristic or property of an entity. If 'Person' is an entity, would the same attributes be used to describe a person in different databases that store medical, student, and fitness club data? Why or why not?

While all three databases might contain the same attributes (such as first name, last name, DoB, phone number, address), different attributes would also be used. A medical database might store the medication a person is on and his/her medical history; a student database might store the classes he/she takes and their grades; and a fitness club database might store his/her date of registration.

Why is data independence desirable?

Without data independence, updating the database might be a arduous task, and it might discourage management from changing the database, even if the organization could benefit from the new information.