UseCase: FindQSOsByPosition

PrimaryActor:

Astronomer.

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EndResult:

List of positions of QSOs. Overplot of those positions on an image display. In the image display, controls to access other data about the selected QSOs.

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OtherActors:

None.

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PreConditions:

Astronomer wants to find all known QSOs in a certain part of the sky for which central coordinates are known.

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FlowOfEvents:

1. Astronomer queries the whole VO specifying a position, search radius and requiring that only QSO data be returned.
2. System returns a collection of tables, each table listing the parameters for QSOs recorded in one data-product somewhere on the VO; no attempt is made to merge the tables.
3. Astronomer selects some of the tables and displays them as symbol plots in an image display.
4. Astronomer selects some of the displayed objects with the mouse.
5. System reveals the detailed data for the selected objects.

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PostCondition:

Astronomer has (a) received tabular data according to his/her search criteria and (b) sampled the data to see which parts are most useful for further study.

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BasicAssumptions:

• The system knows how to set the constraint "only QSOs" in the query.
• The display tool knows how to plot a table of objects according to celestial positions in the table. Inter alia, this means that it has to be able to find out which columns of the table express the positions.
• Since the number of tables to be sampled may be large, the display allows Astronomer to control which tables are displayed at any time. Table plots may be easily turned on and off in the visula stack. Aladin is good at this.

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AlternativeFlows:

1. At some point in the proceedings,

Astronomer wants the collection of tables merged into one table.

1. System merges the tables initially by taking the union of all columns and all rows.
2. System compacts the table by identifying columns that have the same semantic meaning (e.g. by UniformContentDescriptor^?), converting all the data of these colums to the same representation (i.e. harmonizing the units) and then removing the duplicate columns.
3. System compacts the table by merging rows that refer to the same object. Since QSOs are a sparse population on the sky, a simple positional match is sufficient.
4. System presents the merged table to Astronomer.

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Notes:

This case was written as an example of something useful that a VO prototype based on Vizer and Aladin could actually do! Most of the other use cases are way too hard for the prototype.

In fact, there are two subsidiary use cases here: QueryByObjectTypeAndPosition^? and SampleQueryResultsWithDisplay^?, which perhaps ought to be factored out as they are more general and reusable.

The catalogue merging in the alternate flow could also be a use case in its own right. Is this latter case useful enough to be worth working on?

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Links to ScienceProblems:

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KeyReferences:

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GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Use Cases Forum.
Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.

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-- GuyRixon - 08 Feb 2002