Chapter 9 Flashcards
Database management system (DMBS)
a collection of tools, features, and interface that enable users to add, update, manage, access, and analyze data, from a user’s point of view, the main advantage of a DBMS is that it offers timely, interactive, and flexible data access. specific DBMS advantages include the following: scalability,
economy of scale,
enterprise-wide application,
stronger standards,
better security,
and data independence
Data manipulation language
a data manipulation language controls database operations, including storing, retrieving, updating, and deleting data. IBM’s DB2, use a DML
schema
the complete definition of a database, including descriptions of all fields, tables, and relationships. one or more subschemas can also be defined. A subschema is a view of the database used by one or more systems or users. A subschema defines only those portions for the data base that a particular system or user needs or is allows to access
Middleware
which is software that integrates different applications and allows them to exchange data. Middleware can interpret client requests in HTML form and translate the requests into commands that the dtabase can execute.
Foreign key
A foreign key is a field in one table that must match a primary key value in another table in order to establish the relationship between the two tables.
Primary Key
a field or combination of fields that uniquely and minimally identifies a particular member of an entity. for example, in a customer table the customer number is a unique primary key because no two customers can have the same customer number. that key is also minimal because it contains no information beyond what is needed to identify the customer. In a CUSTOMER table, a Customer ID might be used as a unique primary key. Customer ID is an example of a primary key based on as single field. a primary key can also be composed of two or more fields.
Normalization
the process of creating table designs by assigning specific fields or attributes to each table in the database. normalization is used to develop an overall database design that is simple, flexible, and free of data redundancy. normalization involves applying a set of rules that can help identify correct inherent problems and complexities in table designs.
The normalization process typically involves four stages; unnormalized design, first normal form, second normal form, and thrid normal form. the three normal forms constitute a progression in which third normal form represents the best design.
first normal form (1NF)
it does not contain a repeating group. to convert an unnormalized design to 1NF, the table’s primary key must be expanded to include the primary key of the repeating group.
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. if any field in a 1NF table depends on only one of the fields in a combination primary key, then the table is not in 2NF.
Third Normal Form (3NF)
A popular rule of thumb is that design is in 3NF if every nonkey field depends on the key, the whole key, and nothing but the key. a 3NF design avoids redundancy and data integrity problems that still can exist 2NF designs. if it is 2NF and if no nonkey field is dependant on another nonkey field. a nonkey field a field that is not a candidate key for the primary key.
Code
A code is a set of letters or numbers that represents a data item. Codes can be used to simplify output, input, and data formats.
Category codes
identify a group of related items. for example, a local department stores uses a two-character category code to identify the department in which a product is sold: GN for gardening supplies, HW for hardware, and EL for electronics.
Derivation codes
combine data from different item attributes, or characteristics. most magazine subscription codes are derivation codes. for example, one popular magazine uses a subscriber’s five-digit postal code, followed by the first, third, and fourth letters of the subscriber’s last name, the last two digits of the subscriber’s house number, and the first, third, and fourth letters of the subscriber’s street name.
Cipher codes
use a keyword to encode a number. A retail store, for example, might use a 10-letter word, such as CAMPGROUND, to code whole sale prices, where the letter C represents 1, A represents 2, and so on. Thus, the code, GRAND, indicates that the store paid $562.90 for the item.
designing codes
keep codes concise
allow for expansion
keep codes stable
make codes unique
use sortable codes
use a simple structure
avoid confusion
make codes meaningful
use a code for a single purpose
keep codes consistent
