Chap 9 Review questions

1. Explain the main differences between a file processing system and a database system.

A database coordinates the physical and logical access to the data; a file-processing system only coordinates physical access to the data.
A DBMS reduces the amount of data duplication.
A DBMS is designed to coordinate and permit multiple users to access data at the same time. A file processing system is much more restrictive in simultaneous data access.

2. What is a DBMS? Briefly describe the components of a DBMS.

A database consists of linked tables that form an overall data structure. A database management system (DBMS) is a collection of tools, features, and interfaces that enable users to add, update, manage, access, and analyze data in a database.
DBMS components include interfaces for users, database administrators, and related systems; a data manipulation language; a schema; and a physical data repository.
3. Describe a primary key, candidate key, secondary key, foreign key, and common field.

 A primary key is a field or combination of fields that uniquely and minimally identifies a particular member of an entity. For example costumer ID can be primary key.
 A candidate key like his name suggest is a key that can be use a primary key but is not use for many reasons. For example social security number can be used as primary key but usually are not use for security reasons might be navigation shortcuts or can trigger other actions.
 A secondary key is a field or combination of fields that can be used to access or retrieve records. Secondary key values are not unique.
 FOREIGN KEY is when a common field exists in more than one table and can be used to form a relationship, or link, between the tables. Most of the time one filed in a table is the primary key in another table.
 A common field is an attribute that appears in more than one entity. Common fields can be used to link entities in various types of relationships.
4. What are entity-relationship diagrams and how are they used? What symbol is used to represent an entity in an ERD? What symbol is used for a relationship? What is cardinality, and what symbols do you use in the crow’s foot notation method?
An entity-relationship diagram (ERD) is a graphic representation of all system entities and the relationships among them. The ERD is based on entities and data stores in DFDs prepared during the systems analysis phase. The relationship between two entities also is referred to as cardinality. A common form of cardinality notation is called crow’s foot notation, which uses various symbols to describe the characteristics of the relationship. The three basic relationships represented in an ERD are one-to-one (1:1), one-to-many (1: M), and many-to-many (M: N).In a M: N relationship, the two entities are linked by an associative entity.
5. What are data warehousing and data mining? Are the terms related?

A data warehouse is an integrated collection of data that can include seemingly unrelated information, no matter where it is stored in the company. Because it can link various information systems and databases, a data warehouse provides an enterprise-wide view to support management analysis and decision making.
Data mining software looks for meaningful data patterns and relationships.
For example, data mining software could help a consumer products firm identify potential customers based on their prior purchases.
Personally I don’t think that those terms are related.
6. What is the criterion for a table design to be in first normal form? How do you convert an unnormalized design to 1NF?
A table is in first normal form (1NF) if it does not contain a repeating group. To convert an unnormalized design to 1NF, you must expand the table’s primary key to include the primary key of the repeating group.
7. What are the criteria for a table design to be in second normal form? How do you convert a 1NF design to 2NF?

A table design is in second normal form (2NF) if it is in 1NF and if all fields that are not part of the primary key are functionally dependent on the entire primary key. First, create and name a separate table for each field in the existing primary key. Next, create a new table for each possible combination of the original primary key fields. Finally, study the three tables and place each field with its appropriate primary key, which is the minimal key on which it functionally depends. When you finish placing all the fields, remove any table that did not have any additional fields assigned to it. The remaining tables are the 2NF version of your original table.
8. What are the criteria for a table design to be in third normal form? How do you convert a 2NF design to 3NF?

A popular rule of thumb is that a design is in 3NF if every nonkey field depends on the key, the whole key, and nothing but the key.
9. Explain the difference between a logical record and a physical record.

A logical record is a related set of field values that describes a single person, place, thing, or event.
A physical record consists of one or more logical records, depending on the blocking factor.

10. How would a specific date, such as September 1, 2011, be represented as an absolute date?

An absolute date is the total number of days from some specific base date. To calculate the number of days between two absolute dates, you subtract one date from the other.