CIS Exam 2

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CIS Exam 2

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Entity
 
- is some identifiable thing that users want to track:
  • Customers
  • Computers
  • Sales
Attribute
 
describe an entity’s characteristics.All entity instances of a given entity class have the same attributes, but vary in the values of those attributes.
DDL
 
Short for Data Definition Language, DDL is a computer language that is used to define data structures. In Database Management Systems (DBMS), it is used to specify a database scheme as a set of definitions (expressed in DDL). In SQL, the Data Definition Language (DDL) allows you to create, alter, and destroy database objects.
Chen Notation
 
Entity relationship model
NULL
 
no legal or binding force; invalid.
Data
 
recorded facts and figures
Data Model
 
is a plan or blueprint for a database design.
  • A data model is more generalized and abstract than a database design.
It is easier to change a data model then it is to change a database design, so it is the appropriate place to work through conceptual database problems

DML
 
data Manipulation language It is used to retrieve, store, modify, delete, insert and update data in database.
Primary Key
 
  • - is a candidate key selected as the primary means of identifying rows in a relation.
    • There is only one primary key per relation.
    • The primary key may be a composite key.
    • The ideal primary key is short, numeric, and never changes.
aggregate functions
 
Aggregate functions perform a calculation on a set of values and return a single value. Except for COUNT, aggregate functions ignore null values. Aggregate functions are frequently used with the GROUP BY clause of the SELECT statement.
Aggregate functions can be used as expressions only in the following:
  • The select list of a SELECT statement (either a subquery or an outer query).
  • A HAVING clause.
Join
 
- Join conditions can be specified in either the FROM or WHERE clauses
Table
 
organizes the information about a single topic into rows and columns
Relationship
 
Entities can be associated with one another
Tuple
 
tuple uniquely identifies a slice of data from a cube. The tuple is formed by a combination of dimension members, as long as there are no two or more members that belong to the same hierarchy.
Derived Attributes
 
- are attributes whose values are generated from other attributes---Something u can calculate from other attributes
Mandatory Participation
 
IF you see a vertical hash mark THEN that entity is mandatory (required) (minimum cardinality of one [ 1]).

SQL
 
Structured Query Language is an internationally recognized standard database language that is used by all commercial DBMSs.
Candidate Key
 
is a key that determines all of the other columns in a relation.
Foreign Key
 
  • is the primary key of one relation that is placed in another relation to form a link between the relations.
    • A foreign key can be a single column or a composite key.
    • The term refers to the fact that key values are foreign to the relation in which they appear as foreign key values.
ER Model
 
a set of concepts and graphical symbols that can be used to create conceptual schemas.
Relation
 
  • - is a two-dimensional table that has the following characteristics:
    • Rows contain data about an entity.
    • Columns contain data about attributes of the entity.
    • All entries in a column are of the same kind.
    • Each column has a unique name.
    • Cells of the table hold a single value.
    • The order of the columns is unimportant.
    • The order of the rows is unimportant.
No two rows may be identical.
Composite Key
 
is a key that consists of two or more columns.
Functional Dependency
 
occurs when the value of one (set of) attribute(s) determines the value of a second (set of) attribute(
Identifier
 
- are attributes that name, or identify, entity instances. The identifier of an entity instance consists of one or more of the entity’s attributes.
Surrogate Key
 
- is an artificial column added to a relation to serve as a primary key.
  • DBMS supplied
    • Short, numeric, and never changes—an ideal primary key
    • Has artificial values that are meaningless to users
    Normally hidden in forms and reports
Key
 
is a combination of one or more columns that is used to identify rows in a relation.
Codds Rules
 
—A Relational Database: —Rows contain data about one entity —Columns contain data about attributes of the entities —All entries in a column are of the same kind —Each column has a unique name —Cells of the table hold a single value (No commas!) —The order of the columns is unimportant —The order of the rows is unimportant —No two rows may be identical —So….you can get to any data if you know the table name, column name, and key attribute —
DBMS
 
—The Database Management System (DBMS) creates, processes, and administers databases.
Primary key
 
is a candidate key selected as the primary means of identifying rows in a relation.
  • There is only one primary key per relation.
  • The primary key may be a composite key.
Identifiers
 
•Identifiers are attributes that name, or identify, entity instances. •The identifier of an entity instance consists of one or more of the entity’s attributes.
Composite identifiers
 
are identifiers that consist of two or more attributes.
Cardinality
 
means “count,” and is expressed as a number. •Maximum cardinality is the maximum number of entity instances that can participate in a relationship. •Minimum cardinality is the minimum number of entity instances that must participate in a relationship.
recursive relationship
 
occurs when an entity has a relationship to itself
Data redundancy- Why is it a problom
 
it creates redundancy, fix it by normalization
Super Key
 
group of all possible keys
View
 
Snap shot of database at one given point
Modification Anomaly (Three kinds)-
 
update, delete, insert
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