INFS 247 Quiz 2

Mapping entities into relations:

(1) Each entity becomes a relation (2) Each attribute of an entity becomes a column of the newly created relation (3) A unique attribute becomes the primary key in the resulting mapped relation.

What is Form of the data base front end?

(1) Enables data input and retrieval for end users (2) Provides an interface into a database relation or query.

What is Maximum Cardinality?

* One: (represented by a straight bar: I) *Many (represented by a crow's foot symbol: >)

What is Minimum Cardinality?

* Optional (represented by a circular symbol: 0) * Mandatory (represented by a straight bar: I)

What are Entities?

Constructs that represent what the database keeps track of. The basic building blocks of an ER diagram. Represent various real world notions, such as people, places, objects, items, and other concepts. Within one ERD each entity must have a different name.

What is a relationship?

ER modeling construct depicting how entities are related. Within an ER diagram, each entity must be related to at least one other entity. via a relationship.

What is Referential integrity constraint?

In each row of a relation containing a foreign key, the value of the foreign key EITHER matches one of the values in a primary key column of the referred relation OR the value of the foreign key is null (empty). A rule that defines values that are valid for use in foreign keys. In a relational schema lines pointing from the foreign key to the corresponding primary key are referred to as referential integrity constraint lines.

What are entity instances (entity members)?

Occurrences of an entity. Each depicted entity contains a number of entity instances or entity members. Entities themselves are depicted in ER diagrams while entity instances are not. Entity instances are eventually recorded in the database that is created based on the ER diagram.

What is Report of the data base front end?

Presents the data and calculations on the data from one or more tables from the database in a formatted way. The data is retrieved via reports is formatted and arranged to be displayed on the screen or printed as a hard copy.

What is Database front-end?

Provides access to the database for indirect use.

What is a relational database model?

a logical database model that represents database as a collection of related tables.

What is an Unique Attribute?

attribute whose value is different for each entity instance. Every regular entity must have at least one attribute. Unique attributes are underlined.

What is a relational database?

collection of related relations within which each relation has a unique name.

What is Primary Key?

column (or set of columns) whose value is unique for each row. Each relation must have a primary key. The name of the primary key column is underlined in order to distinguish it from the other column in the relation.

What is a foreign key?

column in a relation that refers to a primary key column in another (referred) relation. A mechanism that is used to depict relationships in the relational database model. For every occurrence of a foreign key, the relational schema contains a line pointing from the foreign key to the corresponding primary key.

What is Entity-Relationship (ER) modeling?

conceptual database modeling technique. Enables the structuring and organizing of the requirements collection process. Provides a way to graphically represent the requirements.

What are Cardinality Constraints?

depict how many instances of one entity can be associated with instances of another entity.

What are attributes?

depiction of a characteristic of an entity. Represents the details that will be recorded for each entity instances. Within one entity, each attribute must have a different name.

a database can have multiple sets of...

front-end applications for different purposes or groups of end users.

What is entity integrity constraint?

in a relational table, no primary key column can have null (empty) values. Every RBMS enforces this rule.

What are Relationship Instances?

occurrences of a relationship. Occurs when an instance of one entity is related to an instance of another entity via a relationship. Relationships themselves are depicted in the ER diagrams while relationship instances are not. Relationship instances are eventually recorded in the database that is created based on the ER diagram.

Most contemporary commercial DBMS software packages, are.....

relational DBMS (RDBMS) software packages.

Once an ER diagram is constructed, it is....

subsequently mapped into a relational schema (collection of relations).

What is a relation?

table in a relational database. A table containing rows and columns. The main construct in the relational database mode. Every relation is a table, not every table is a relation.

What is an ER diagram?

the result of ER modeling. Serves as a blueprint for the database.

What is a relational schema?

visual depiction of the relational database model. Once database requirements are collected and visualized as an ER diagram, the next step in creating a relational database into convert the ER diagram into a relational schema.