RDH handles a DAP2 data request

Point Of Contact: A Human

Description

Give a short descriptive name for the use case to serve as a unique identifier.

The RDH receives and responds to a bes:get request for DAP2 data.

Goal

The goal briefly describes what the user intends to achieve with this use case.

Summary

Give a summary of the use case to capture the essence of the use case (no longer than a page). It provides a quick overview and includes the goal and principal actor.

Actors

List actors, people or things outside the system that either acts on the system (primary actors) or is acted on by the system (secondary actors). Primary actors are ones that invoke the use case and benefit from the result. Identify sensors, models, portals and relevant data resources. Identify the primary actor and briefly describe role.

Preconditions

Here we state any assumptions about the state of the system that must be met for the trigger (below) to initiate the use case. Any assumptions about other systems can also be stated here, for example, weather conditions. List all preconditions.

Triggers

Here we describe in detail the event or events that brings about the execution of this use case. Triggers can be external, temporal, or internal. They can be single events or when a set of conditions are met, List all triggers and relationships.

Basic Flow

Often referred to as the primary scenario or course of events. In the basic flow we describe the flow that would be followed if the use case where to follow its main plot from start to end. Error states or alternate states that might be highlighted are not included here. This gives any browser of the document a quick view of how the system will work. Here the flow can be documented as a list, a conversation or as a story.(as much as required)

1. The BES receives from a BES client a request containing bes:get command for a DAP2 data response for data help by a Data Source in the RDH:

   <?xml version="1.0" encoding="UTF-8"?>

   <bes:request xmlns:bes="http://xml.opendap.org/ns/bes/1.0#" reqID="[http-8080-2:17:bes_request]">

      <bes:setContext name="xdap_accept">2.0</bes:setContext>

      <bes:setContext name="dap_explicit_containers">no</bes:setContext>

      <bes:setContext name="errors">dap2</bes:setContext>

      <bes:setContainer name="catalogContainer" space="catalog">/data/stuff/dataSourceOne</bes:setContainer>

      <bes:define name="d1" space="default">

        <bes:container name="catalogContainer" />

      </bes:define>

      <bes:get type="dods" definition="d1" />

   </bes:request>

   Make sure to update this to match what we actuall use! ndp 16:27, 28 April 2009 (PDT)

2. In the BES, the RDH is identified as the service will provide the requested DAP2 data.
3. The RDH determines which ODBC Data Source is associated with the requested DAP2 data.
4. The RDH uses the ODBC introspection API to get the structural (do i mean schema here? ndp) descriptions of the tables and views held by the ODBC Data Source.
5. The RDH instantiates/constructs a DDS class instance in memory that reflects the DAP data model representation of the tables and views held by the ODBC Data Source using the information collected in the previous step.
6. The RDH applies any constraint expression to the DDS instance. (marks all of the projected variables).
7. The RDH converts the constraint expression (or the lack of one if none is present) into one or more SQL query strings.
8. The RDH uses the ODBC API to send the SQL query string(s) to the Data Source.
9. The RDH uses the ODBC API retrieve the row set(s) returned.
10. The RDH uses the ODBC API and the DDS instance to serialize the DAP2 data response to the BES client, while applying any as yet unresolved query conditions (conditions that were not converted into part of the SQL query string(s).)

Alternate Flow

Here we give any alternate flows that might occur. May include flows that involve error conditions. Or flows that fall outside of the basic flow.

Post Conditions

Here we give any conditions that will be true of the state of the system after the use case has been completed.

Activity Diagram

Here a diagram is given to show the flow of events that surrounds the use case.

Notes

There is always some piece of information that is required that has no other place to go. This is the place for that information.

Resources

In order to support the capabilities described in this Use Case, a set of resources must be available and/or configured. These resources include data and services, and the systems that offer them. This section will call out examples of these resources.

Resource	Owner	Description	Availability	Source System
name	Organization that owns/ manages resource	Short description of the resource	How often the resource is available	Name of system which provides resource