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@ []Query Q 2.6.1: Find the current Toy department data
Answer: ``(Toy, Di, $100K).''
Category: (Complete, None) /
(Containment, Event, Explicit) /
(=, Constant)
The current manager and budget of the Toy department are Di and $100K, respectively.
The temporal selection predicate ``(Containment, Event, Explicit)'' selects the department data whose valid-time includes the explicit event ``now.'' A non-temporal predicate in the category ``(=, Constant)'' selects Toy data.
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@ []Query Q 2.6.2: Find the skills for which Ed was qualified after 1/1/83
Answer: ``filing'' and ``driving.''
Category: (Projected, None) / (Ordering, Event, Explicit) / (=, Constant)
Ed was qualified for filing on 1/1/85 and for driving (for the second time in his career) on 6/1/84. The valid-time selection predicate ``(Ordering, Event, Explicit)'' compares the valid-time of Ed's skills with the explicitly supplied event 1/1/83. The non temporal predicate selects Ed's data in the skills relation.
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@ []Query Q 2.6.3: Find Di's salary on her 25th birthday
Answer: ``$40K.''
Category: (Projected, None) /
(Containment, Event, User-defined) /
(=, Constant)
The date of Di's 25th birthday is 10/1/85. At that time her salary was $40K.
The valid-time selection embedded in the query is categorized as ``(Containment, Event, User-defined),'' since it selects employee data whose valid-time contains an event computed from the user-defined time attribute D-birth. Two non-temporal selections in the category ``(=, Constant)'' are used to select employees whose name is ``Di'' (once to select her D-birth and once to select her Salary).
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@ []Query Q 2.6.4: Find the departments Ed worked in before and not after 1/1/88
Answer: ``Toy.''
Category: (Projected, None) /
(Ordering, Event, Explicit) /
(=, Single)(=, Constant)
Before 1/1/88 Ed worked only in the Toy department (from 2/1/82 to 1/31/87).
The query can be answered in two steps. At first, the names of all the departments Ed worked in are selected by means of a ``(=, Const)'' non-temporal predicate. In the second step, each name is used to find out the temporal element in which Ed worked in such a department by means of a ``(=, Single)'' non-temporal predicate. Finally, the department name is retrieved only if the temporal element precedes the event-valued constant 1/1/88 according to an ``(Ordering, Event, Explicit)'' temporal selection predicate.
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@ []Query Q 2.6.5: Find the name and date of birth of the women who were working
in the Toy department on 1/1/83
Answer: ``(Di, 10/1/60).''
Category: (Projected, None) /
(Containment, Event, Explicit) /
(=, Constant)
The only woman working in Toy department on 1/1/83 was Di. Di was born on 10/1/60.
The categorization of the query as ``(Containment, Event, Explicit)'' indicates that employee data are selected if their valid-times contain the event 1/1/83, explicitly supplied in the query. Furthermore, the non-temporal clause selects only female employees working in the Toy department.
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@ []Query Q 2.6.6: Who worked in their current department longer than their current
manager?
Answer: ``None''
Category: (Projected, None) / (Containment, Event, Explicit) /