Lesson 3 Flashcards
Domain
In data modeling, the construct used to organize and describe an attribute’s set of possible values.
Key
One or more attributes that determine other attributes.
What are the types of keys?
- Superkey
- Candidate key
- Primary key
- Secondary key
- Foreign key
Primary key
In the relational model, an identifier composed of one or more attributes that uniquely identifies a row. Also, a candidate key selected as a unique entity identifier.
Determination
- The role of a key
- In the context of a database table, the statement “A determines B” indicates that knowing the value of attribute A means that the value of attribute B can be looked up.
Functional dependence
- Within a relation R, an attribute B is functionally dependent on an attribute A if and only if a given value of attribute A determines exactly one value of attribute B.
- The relationship “B is dependent on A” is equivalent to “A determines B,” and is written as A -> B.
Determinant
Any attribute in a specific row whose value directly determines other values in that row
Dependent
An attribute whose value is determined by another attribute
Full functional dependence
A condition in which an attribute is functionally dependent on a composite key but not on any subset of the key.
Composite key
A multiple-attribute key
Key attributes
The attributes that form a primary key
Superkey
An attribute or attributes that uniquely identify each entity in a table.
Candidate key
A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey.
Entity integrity
The property of a relational table that guarantees each entity has a unique value in a primary key and that the key has no null values.
Null
The absence of an attribute value. Note that a null is not a blank.
Foreign key (FK)
An attribute or attributes in one table whose values must match the primary key in another table or whose values must be null.
Referential integrity
A condition by which a dependent table’s foreign key must have either a null entry or a matching entry in the related table.
Secondary key
- A key used strictly for data retrieval purposes.
- For example, customers are not likely to know their customer number (primary key), but the combination of last name, first name, middle initial, and telephone number will probably match the appropriate table row.
What are the 3 types of referential integrity rules?
- Delete
- Insert
- Update
Flags
- Special codes implemented by designers to trigger a required response, alert end users to specified conditions, or encode values.
- Flags may be used to prevent nulls by bringing attention to the absence of a value in a table.
Composite entity
An entity designed to transform an M:N relationship into two 1:M relationships. The composite entity’s primary key comprises at least the primary keys of the entities that it connects.
What are the other names that refer to the definition of “composite entity”?
- Bridge entity
- Associative entity
Linking table
- In the relational model, a table that implements an M:M relationship.
- In other words, a linking table is the implementation of a composite entity.
Index
An ordered array of index key values and row ID values (pointers). Indexes are generally used to speed up and facilitate data retrieval.
_____ ____ can also be referred to as a index
Index key
Unique index
An index in which the index key can have only one associated pointer value (row).
The practical significance of taking the logical view is that it serves as a reminder of the simple file concept of data storage. (T/F)
True
You can think of a table as a persistent representation of a logical relation.
True
The order of the rows and columns is important to the DBMS.
False
Character data type also known as string data type, can contain any character or symbol not intended for mathematical manipulation, but character sets can include digits or a numeric string. (T/F)
True
A candidate key is a minimal superkey without any unnecessary attributes. (T/F)
True
Each table _____ represents an attribute.
Column
Date attributes contain calendar dates stored in a special format known as the _____ date format.
Julian
A table is also called a _____ because the relational model’s creator, E. F. Codd, used the two terms as synonyms.
Relation
In a relational table, each column has a specific range of values known as the ______ domain.
Attribute
_____ logic, used extensively in mathematics, provides a framework in which an assertion (statement of fact) can be verified as either true or false.
Predicate
Primary keys are required in relational databases to ensure entity integrity. (T/F)
True
The idea of determination is unique to the database environment. (T/F)
False
Only a single attribute, not multiple attributes, can define functional dependence. (T/F)
False
If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that composite key, the attribute (B) is fully functionally dependent on (A). (T/F)
True
A null is created when you press the Enter key or the Tab key to move to the next entry without making a prior entry of any kind. (T/F)
True
Depending on the sophistication of the application development software, nulls can create problems when functions such as COUNT, AVERAGE, and SUM are used. (T/F)
True
In the relational model, _____ are important because they are used to ensure that each row in a table is uniquely identifiable.
Keys
A _____ is a key that can uniquely identify any row in the table.
Superkey
A _____ key can be described as a minimal superkey, a superkey without any unnecessary attributes.
Candidate
A _____ is the primary key of one table that has been placed into another table to create a common attribute.
Foreign key
A _____ key is defined as a key that is used strictly for data retrieval purposes.
Secondary
When you define a table’s primary key, the DBMS automatically creates a(n) _____ index on the primary key column(s) you declared.
Unique
In a relational model, ____ are also used to establish relationships among tables and to ensure the integrity of the data.
Keys
A primary key is a _____ key selected to uniquely identify all other attribute values in any given row.
Candidate
A table is also called a relation because the relational model’s creator, E. F. Codd, used the two terms as __________.
Synonyms
A ______ is perceived as a two-dimensional structure composed of rows and columns.
Table
The word ______, also known as a dataset in Microsoft Access, is based on the mathematical set theory from which Codd derived his model.
Relation
Rows are sometimes referred to as __________.
Records
The CUSTOMER table’s primary key is CUS_CODE. The CUSTOMER primary key column has no null entries, and all entries are unique. This is an example of _____ ______.
Entity Integrity
Referential _____ dictates that the foreign key must contain values that match the primary key in the related table, or must contain null.
Integrity
The _____ constraint can be placed on a column to ensure that every row in the table has a value for that column.
NOT NULL
To avoid nulls, some designers use special codes, known as _____, to indicate the absence of some value.
Flags
RDBMSs enforce integrity rules automatically. (T/F)
True
The one to many (1:M) relationship is easily implemented in the relational model by putting the foreign key of the “1” side in the table of the “many” side as a primary key. (T/F)
False
As rare as 1:1 relationships should be, certain conditions absolutely require their use. (T/F)
True
The _____ relationship is the “relational model ideal.”
1:M
The _____ relationship should be rare in any relational database design.
1:1
_____ relationships can be implemented by creating a new entity in 1:M relationships with the original entities.
M:N
Another name for a composite entity is a(n) _____ entity.
Bridge
The ___ relationship is the relational database norm.
1:M
____ relationships cannot be implemented as such in the relational model.
M:N
If one department chair “a professor” can chair only one department, and one department can have only one department chair. The entities PROFESSOR and DEPARTMENT exhibit a ___ relationship
1:1
One characteristic of generalization hierarchies is that they are implemented as ____ relationships.
1:1
The proper use of ______ keys is crucial to controlling data redundancy.
Foreign
Proper data ________ design requires carefully defined and controlled data redundancies to function properly.
Warehousing
The database designer has two main options when defining a composite table’s primary key: use the combination of foreign keys or create a new primary key. (T/F)
True
A(n) _____ is an orderly arrangement used to logically access rows in a table.
Index
A ______ index is an index in which the index key can have only one pointer value (row) associated with it.
Unique
An index key can have multiple _______ (a composite index).
Attributes
