active: Programs

NetKernel uses the active: scheme to specify programs in the form of a URI address and resource identifier.

At first glance, it would seem that the set of verbs in NetKernel is small and potentially constraining. However, the verbs are general indicators of intent and work at the level of the resource abstraction. Within and behind the URI there is essentially unlimited programming power. For example, the active: scheme allows for the specification of a program as a URI address and Script Programs support arbitrary sequencing of URI requests.

The active: scheme is a standards compliant URI scheme that supports the specification of a service and an unlimited number of named parameters. The general form is

active: {service-name} ["+" {parameter-name} "@" {parameter-value-URI}]+

for example, the following specifies an XSLT transform:

active:xslt+operator@ffcpl:/src/style.xsl+operand@ffcpl:/context.xml

When a SOURCE request for the above URI is issued, the XSLT service is invoked with the supplied parameters. Note that the two ffcpl: scheme URIs will be processed by NetKernel as sub-requests. In fact, the parameter values could be supplied by their own active: scheme URI addresses which means tree-structured programs can be composed.

The active: scheme approach to specifying programs is essentially a functional programming environment. Because the syntax required to define active: scheme programs can get involved DPML can be used to simplify their definition and provide rudimentary sequencing.