Term
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Definition
A relation is a special case of a table, where a table may not necessarily be of a relation. The characteristics of a Relationship are:
- Rows contain data about an "entity".
- Columns contain data about attributes of the ^
- All entries in a column are of the same knd.
- 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
- Now two rows may be identical
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Term
| What is a functional dependency? |
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Definition
A relationship between attributes in which one attribute or group of attributes determines the value of another.
(e.g., The expression X ---> Y means that given a value of X, we can determine the value of Y) |
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Term
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Definition
An attribute or group of attributes that identifies a unique row in a relation.
One of the candidate keys is chosen to be the primary key. |
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Term
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Definition
One or more attributes that functionally determine another attribute or attributes.
(E.g., in the Functional Dependency (A,B)--->C, the attributes (A,B) are the "determinants." |
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Term
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Definition
| A key with 2 or more attributes (columns) |
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Term
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Definition
A candidate key selected to be the key of relation.
A primary key is used as a foreign key for representing relationships. |
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Term
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Definition
A unique, sysgtem-supplied identifier used as the primary key of a relation.
It is created when a row is created, it never changes, and it is destroyed when the row is deleted.
The values of a surrogate key have no meaning to the users and are usually hidden within forms and reports. |
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Term
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Definition
An attribute that is a key of one or more relations other than the one in which it appears.
It is used to represent relationships.
It's constraint creates relationships and referential integrity between tables. |
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Term
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Definition
A rule or set of rules governing the allowed structure of relations.
The rules apply to attributes, functional dependencies, multivalue dependencies, domains, and constraints.
The most important forms are the first normal form, second normal form, and third normal form. |
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Term
| What is a multivalued dependency? |
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Definition
A condition in a relation with three or more attributes in which independent attributes appear to have relationships they do not.
No time for an example! |
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Term
| Suppose that two columns in two different tables have the same column name. What convention is used to give each a unique name? |
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Definition
| Typing in the name of the table, followed by a period, and then the column name |
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Term
Explain the meaning of this functional dependency:
PartNumber ----> PartWeight |
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Definition
| The value of PartNumber will determine the value of PartWeight. |
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Term
Explain the meaning of the expression:
(FirstName, LastName) ---> Phone |
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Definition
| FirstName and LastName functions as a composite determinant, that will determine the value of Phone |
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Term
If (A,B)---> C, can we also say
A---> C ? |
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Definition
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Term
| If A ---> (B,C), then can we also say that A ---> C ? |
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Definition
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Term
Is it true that
PartNumber ---> PartWeight |
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Definition
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Term
| Under what conditions will a determinant be unique in a relation? |
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Definition
| A determinant is unique in a relation only if it determines every other column in the relation. |
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Term
Illustrate deletion, modification, and insertion anomalies on the STUDENT_ACTIVITY relation in the following figure:
[image]
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Definition
[image]
Deletion Anomaly - Deleting Clibming Club from row 4 will delete all information about Garrett.
Update Anomaly - Changing the cost of Scuba Club in row 1 will leave the cost of Scuba Club in row 2 at the old price.
Insertion Anomaly - Entering in the amount paid by Jones in row 1 would require knowing the value of every other field as well, rather than just knowing how much Jones is paying. |
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Term
| What conditions are required for a relation to be BCNF? |
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Definition
| For a condition to be BCNF the relations must be one in which every determinant is a candidate key and the relation must be 3NF. |
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Term
| What is a referential integrity constraint? |
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Definition
| A referential integrity constraint is a statement that limits the values of the foreign key |
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Term
Explain the role of referential integrity constraints in normalization
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Definition
Normalizing a relation can require creating new relations with the determinant, causing the problem as the new foreign key.
Referential integrity constraint specifies that the values of a foreign key must be a subset of values of the primary key, to which it refers. |
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Term
In normalization example 4, under what constraint is:
(SID, CLUB) ---> Cost
more accurate than
CLUB ---> Cost |
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Definition
| If a student has a membership or some other variable is applied that would make the cost of the CLUB unique to that student, then knowing the SID and Club name would make the Cost value more accurate. |
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