Name: DPML Description: The active:dpml service is the DPML runtime engine which executes DPML scripts Id: DPMLRuntime Category: accessor Identifier Syntax DPML is an accessor using Active URI syntax with the following base identifiers: Base active:dpml and the following arguments: (for more details on argument passing details see here) Argument Rules Typing Description operator Mandatory Representation (java.lang.Object) The DPML program script to be executed response Optional Representation (java.lang.Object) The internal assignment returned as the response from the script execution varargs [varargs] Any quantity Representation (java.lang.Object) Varargs allows an arbitrary number of additional unspecified arguments. Request Verbs The following verbs are supported: Verbs SOURCE SINK EXISTS DELETE NEW Response The response representation of this accessor for SOURCE requests is unknown. This accessor throws no documented exceptions. Import Requirements To use DPML accessor you must import the module urn:org:netkernel:lang:dpml: <import>   <uri>urn:org:netkernel:lang:dpml</uri> </import>

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The Declarative-Request Process Markup Language (DPML), is a simple, lightweight language. With DPML you can write programs that directly request information resources and leverage various resource models without knowledge of low-level APIs and objects.

SOURCE

When a request with the SOURCE verb is issued to active:dpml the DPML script specified in the required operand argument is brought into the DPML language runtime environment. A request is then made for the assignment made to response (unless another assignment is specified by the optional response argument).

If the root element of the DPML script is a closure, then the closure with the specified assignment is evaluated and its response is returned as the response to the SOURCE request.

If the root element of the DPML script is a sequence, then the child elements of a sequence are evaluated in order. If during this evaluation an assignment is made to response, this is returned, if no assignment is made to response the null is returned.

Arguments may be passed into the DPML script by including one or more optional additional arguments. These additional argument are available to the script through the arg: URI scheme.

Example - Closure

This DPML script uses a closure as the root element and includes two closures with their assignments. By default, the closure with the assignment to response is evaluated and returned.

The following code will cause the variable answer to contain the text value Response:

request = context.createRequest("active:dpml");
request.addArgument("operand", "res:/scripts/closures.dpml")
answer = context.issueRequest(request);

While the following code will cause the variable answer to contain the text value Output:

request = context.createRequest("active:dpml");
request.addArgument("operand", "res:/scripts/closures.dpml")
request.addArgumentByValue("response", "output")
answer = context.issueRequest(request);

Example - Sequence

This DPML script uses a sequence as the root element which includes two requests. Both make an assignment to response. The requests are evaluated in document order and only the final assignment to response is made available to the external client.

When the following code is executed, the variable answer will be set to the evaluation of the second request which provides contents of the resource res:/second.txt.

request = context.createRequest("active:dpml");
request.addArgument("operand", "res:/scripts/sequence.dpml")
answer = context.issueRequest(request);

Example - Arguments

This DPML script contains a request for a resource identified by the value of an optional argument named resource.

When this is executed by the DPML runtime using the following code:

request = context.createRequest("active:dpml");
request.addArgument("operand", "res:/scripts/program2.dpml")
request.addArgument("resource", "res:/greeting.txt")
answer = context.issueRequest(request);

The variable answer will be set to the contents of the resource identified by the resource argument.

SINK

When a request with the SINK verb is issued to active:dpml the DPML script specified in the required operand argument is brought into the DPML language runtime environment. The processing is identical to the processing for the SOURCE verb except that the value of arg:verb is set to the text value SINK. The representation passed in this request as the primary argument is available as arg:primary.

NEW

When a request with the NEW verb is issued to active:dpml the DPML script specified in the required operand argument is brought into the DPML language runtime environment. The processing is identical to the processing for the SOURCE verb except that the value of arg:verb is set to the text value NEW.

EXISTS

When a request with the EXISTS verb is issued to active:dpml the DPML script specified in the required operand argument is brought into the DPML language runtime environment. The processing is identical to the processing for the SOURCE verb except that the value of arg:verb is set to the text value EXISTS.

DELETE

When a request with the DELETE verb is issued to active:dpml the DPML script specified in the required operand argument is brought into the DPML language runtime environment. The processing is identical to the processing for the SOURCE verb except that the value of arg:verb is set to the text value DELETE.