Chapter 2 - Database Management Systems
What is a query-by-example (QBE)?
A data manipulation language for relational databases in which users indicate the action to be taken by completing on-screen forms
What is Null?
A data value meaning "unknown" or "not applicable".
What is a computed field (calculated field)?
A field whose value is computed from other fields in the database; also called a calculated field.
What is an aggregate function (function)?
A function used to calculate the number of entries, the sum of average of all the entries in a given column, or the largest or smallest of the entries in a given column; also called function.
What is a primary key?
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. Also see candidate key
What is a delete query?
A query that deletes all records that satisfy some criterion.
What is relational algebra?
A relational data manipulation language in which new tables are created from existing tables through the use of a set of operations.
What is a criterion?
A statement that can be either true or false. In queries, only records for which the statement is true will be included; also called a condition.
What is a unnormalized relation?
A structure that satisfies the properties required to be a relation (table) with the exception of allowing repeating groups (the entries in the table do not have to be single-valued).
What is a Relation?
A two-dimensional table-style collection of data in which all entries are single-valued, each column has a district name, all the values in a column are values of the attribute that is identified by the column name, the order of columns is immaterial, each row is distinct, and the order of rows is immaterial. Also called a table.
What is a make-table query?
An Access query that creates a table using the results of a query.
What is a relational operator (comparison operator)?
An operator used to compare values. Valid operators are =, <, >, <=, >=, < >, and !=. Also called a comparison operator.
What is an AND criterion?
Combination of criteria in which both criteria must be true.
What is an update query?
In Access, a query that updates the contents of a table
What is a join line?
In an Access query, the line drawn between tables to indicate how they are related.
What is concatenation?
The combination of two or more rows in an operation, such as a join, or the combination of two or more columns for a primary key field to uniquely identify a given row in the table.
What is a sort key?
The field on which data are sorted; also called a key.
What is a outer join?
The form of a join in which all records, even if they don't match.
What is a tuple?
The formal name for a row in a table.
What is a natural join?
The most common form of a join.
What is a WHERE clause?
The part of an SQL SELEC command that indicates the condition rows must satisfy to be displayed in the query results.
What is a criteria?
The plural version of the word criterion.
What is a design grid?
The portion of the Query Design window in Access where you enter fields, criteria, sort orders, and so on
What is grouping?
The process of creating collections of records that share some common characteristic.
What is sort?
The process of creating collections of records that share some common characteristic.
What is SUBTRACT?
The relational algebra command for performing the difference of two tables.
What is INTERSECT?
The relational algebra command for performing the intersection of two tables.
What is Division?
The relational algebra command that combines tables and searches for rows in the first table that match all rows in the second table.
What is SELECT?
The relational algebra command to select rows from a table. Also, the retrieval command in SQL.
What is PROJECT?
The relational algebra command used to select columns from a table.
What is product?
The table obtained by concatenating every row in the first table with every row in the second table.
What is a Cartesian product?
The table obtained by concatenating every row in the first table with every row in the second table. It is called a different name in mathematical.
What is a qualify?
To indicate the table (relation) of which a given column (attribute) is a part by preceding the column name with the table name. For example, Customer.Address indicates the column named Address in the table named Customer.
What is a compound criteria (Compound Condition)?
Two simple criteria (conditions) in a query that are combined with the AND or OR operators.
What is union compatible?
Two tables are union compatible if they have the same number of fields and if their corresponding fields have identical data types.
What is an OR criterion?
A combination of criteria in which at least one of the criteria must be true.
What is union?
A combination of two tables consisting of all records that are in either table.
What is a join column?
The column on which two tables are joined.
What is a relational database?
A collections of relations.
What is an attribute?
A characteristic or property of an entity; also called a field or column.
What is a field?
A characteristic or property of an entity; also called an attribute or a column.
What is a record?
A collection of related fields; can be thought as a row in a table.
What is a repeating group?
More than one entry at a single location in a table.
What is intersection?
When comparing tables, an intersection is a new table containing all rows that are in both original tables.
What is difference?
When comparing tables, the set of all rows that are in the first table that are not in the second table.
What is a secondary sort key (minor sort key)?
When sorting on two fields, the less important field; also called minor sort key.
What is a primary sort key (major sort key)?
When sorting on two fields, the more important field; also called a major sort key.
