Databases 1 Flashcards
what is a database?
its a collection of data items structured so that data can be searched and retrieved when necessary
what is a flat file?
the entire base is stored in a single file and there is one row for each record and one column for each field
what is data duplication?
this is the duplication of data
what is data inconsistency?
the more often data has to be keyed the more chance there is for errors in data entry
what is poor data integrity?
data that is erroneous or inconsistent is not reliable
why is relationship databases more powerful?
its a more powerful way of storing data as the relationships allow data to be retrieved from a number of tables using a single query and there is less data redundancy
what is a primary key?
consists of more than one attribute that identifies one record from any other
what is a foreign key?
its a primary key in one entity which is included in another entity to link the two tables
how are relationships formed?
foreign keys that link tables together
constraint’s help control data integrity and fix problems such as:
entering project name in a field where a project name is expected
having two projects with the same project ID
maintaining data integrity
what does the features of constraints provide?
allows us to set field properties, link tables and set constraints help to increase the reliability of the data
what are some of the operations that can be allowed or disallowed to a user?
SELECT
INSERT
DELETE
ALTER
CREATE
what can SQL allow you to do?
allows most users to query and manipulate data, as well as protect it from unwanted updates, deletions or other errors
what is the relational models portability?
its standard
by adhering to the rules of the relational model you ensure that your data can be transferred between relational database systems relatively easily
what is an attribute?
an individual data item within an entity.
what in entity?
identifies an object about which data will be stored within the system
what is composite key?
consists of more than one attribute to uniquely identify an entity occurrence or record
what is a relationship?
its an established by a foreign key in one entity linking to the primary key in another
what is referential integrity?
it ensures that data in one table does not contradict the data in another table
what is data design?
identifying the relationship between data and creating a logical design which is best suited to the data required for a system
what are the steps in designing a database?
first is to identify and state what data needs to be stored
from the statement of data requirements a conceptual data model is produced
what is a logical data model?
when creating a logical data model entities and their relationships are identified with the keys. the attributes of each entity are also identified
a logical data model does not describe the physical structure of the real database
what is a physical data model?
its derived from the logical data model and includes the specification of all tables and the columns inside them.
the physical data model contains the primary keys of each table and it specifies the relationship between the tables using foreign keys
