O Pe NDAP Actor Use Case 01

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Name: Importing DAP data into Kepler.

Version:

1.0.0 Initial draft

1.0.1 Minor edits. Since were writing this after the fact, we might as well skip the future-tense.

Summary:

A user imports DAP data into Kepler. The data is available in the Kepler data model for further processing.

Actors:

• User.
• Kepler software application
• OPeNDAP Kepler "Actor"
• A server on the web with DAP accessible data.

Preconditions:

• User has a complete DAP data URL that accesses and subsets the data that they wish to use.
• The data URL SHOULD subset array variables such that they are reduced to 1 or 2 effective (See Note 01)) dimensions.

Triggers:

Basic course of events:

1. The user starts the Kelper application.
2. The user creates a new Kepler Workflow.
3. The user adds an instance of the OpendapDataSource Actor to the Workflow.
4. The user configures the OpendapDataSource Actor by:
1. Right-clicking on it and selecting "Configure Actor" from the Actor's pop-up menu. This causes a window containing a form to appear. The form has two text fields.
2. The user enters the data URL for the DAP dataset that they wish to access in the first text field. This URL must not contain the

1. The user then enters the constraint expression (CE) that subsets the data set into the second text field. (See Note 02) The CE may be null.
2. The user presses the "Commit" button in the configuration window.
1. The OpendapDataSource Actor reconfigures it's output terminals to reflect the variables specified in the CE.

Alternative Paths:

Exisiting Workflow:

2. The user opens a Workflow stored in a file.
3. Goto Step 4. (Main Path)

Postconditions:

1. DAP data is available to Kepler actors by connecting to the data

1. The User connects one or more of these data source terminals

Business Rules:

Notes:

1. Multidimensional arrays can be subset so that their "effective" dimensionality is reduced by specifying (in the DAP constraint expression) a single index for one or more of the array's dimensions.
   
   
2. The CE is made up of a "projection" and a "selection". The "projection" specifies which variables in the data set the user wishes to access. The "selection" is a series of clauses that specify which conditions data must meet. If the user requests array variables then they SHOULD provide a CE that subsets them in order to reduce their effective dimensions to 1 or 2. Arrays of 1 or 2 dimensions can be represented efficintly in the Kepler data model as a MatrixToken.

Author

Nathan Potter, 12/05/2007