Chapter 4 part 2 Flashcards
Data dictionary
contains information about the structure of the database
Data definition language (DDL)
builds the data dictionary, creates the database, describes logical views for each user, and specifies records or field security constraints
Data manipulation language (DML)
changes database content, including data element updates, insertions, and deletions
Data query language (DQL)
contains powerful, easy-to-use commands that enable users to retrieve, sort, order, and display data
Report writer
simplifies report creation
Relational data model
represents conceptional- and external-level schemas as if data are stored in tables
A tuple
is row in a table that contains data about a specific occurrence of the type of entity represented by that table
Primary key
database attribute, or combination of attributes, that uniquely identifies a specific row in a table
Foreign key
an attribute that is a primary key in another table, that is used to link tables
Disadvantages of storing data in one table
update anomaly
insert anomaly
delete anomaly
Update anomaly
not correctly recorded data value. example, updating an address of a costumer means that the whole tabel has to be searched to change them one by one
Insert anomaly
Only a way on inserting a new entity is when there is an action. example, a person has to by a product so that he goes on record
Delete anomaly
deleting a row has unintended consequences. example, deleting the row of a costumer who only purchased one item means deleting all the information of that costumer
Requirements of a relational database
- every column in a row must be single valued
- primary keys cannot be null
- foreign keys, if not null, must have values that correspond to the value of a primary key in another table
- all nonkey attributes in a table must describe a characteristic of the object identified by the primary key
