a structure that can store information about multiple types of entities, the attributes of these entities, and the relationships among the entities
a person, place, object, event, or idea for which you want to store and process data
a characteristic or property of an entity; also a field or a column
an association between entities
DBMS(database management system)
a program, or a collection of programs through which users interact with a database. lets you create forms and reports quickly and easily, as well as obtain answers to questions about the data stored in a database
a minimal collection of columns (attributes) in a table on which all columns are functionally dependent and that is chosen as the main direct-access vehicle to individual rows
field linking two tables
a characteristic or property of an entity; also called an attribute or a column
a collection of related fields; can be though of as a row in a table
lets you change structure of database without requiring you to change
programs to access database (forms and reports interacting with
programmer needs to update programs to match the new database structure (may just avoid changing database all together)
duplication of data or storing of the same data in more than one place
problems of data redundancy
wastes space, takes up memory, takes up time, have to fix each occurence, inconsistencies
steps to design database
1) Analysis of requirements, 2) Design 3) Implementation (Logical and Physical Design)
Can a table represent more than one entity?
each entity has its own table
an attribute that specifies the type of data that the object can hold
replaces paper file, file used to store data
When does a database have integrity?
when the data follows all the rules (or meets all the integrity constraints)
What is another term for a table?
What is another term for rows?
What is a weak entity?
depends on another entity for its existence
(cannot be created without proper parent, if parent is deleted, delete weak entity)
What are the rules used to identify keys?
1) Choose key that will not change value over life of each instance of an entity type
Why is a table with a single attribute in its
primary key automatically in 2nf?
no repeating groups, no nonkey column depends on only a portion of the primary key
Is the conceptual model dependent on
collection of entities that share common properties or characteristics
Do supertype and subtypes share common
yes, common attributes or relationships
ERD and Normalization are a part of which design?
What is a recursive relationship?
urnary relationship, degree of 1- relationship between instances of 1 entity type; 1:1, 1:M, M:N
What does a minimum cardinality of 0 mean?
Minimum cardinality of 1?
How are M:N relationships dealt with?
1 entity relates to many instances of another entity; must be separated into additional 1:M relations >> intersection relation (keys would be made up of parent keys
What do ERDs show?
logical representation of the data of an organization(entities), relationships among entities, attributes of entities
a single entity instance of one entit type is related to a single entity instance of another type, primary key of one would be foreign key in the other; key of either table can be placed as a foreign key in the other table
a signle instance of one entity related to many instances of another entity, Parent-child relationship
Parent child relationship
Parent is one side (Primary table) , child is the many side (related table), place parent key of parent table in child table
generic entity type subdivided into subtypes
subset of a supertype that shares common attributes or relationships distinct from other subsets
an entity in the entity-relationship model used to implement a many-to-many relationship
an entity that requires a relationship to another entity for identification
an entity that does not require a relationship to another entity for identification
what is ERM used for?
allows us to identify relationships between entities
an attribute can have more than one value for each entity instance (or repeating groups) removed during normalization process in logical design, become entities of their own