Summary

This recipe shows how to convert a flow (expressed in RDF) into an equivalent ZigZag script automatically.

A simple flow example

To introduce some of the ZigZag concepts we will use the following flow

Example flow that concatenate strings and converts the result into upper case

This flow is available on any Meandre engine as part of the /public/services/demo_repository.rdf. If we run the flow from the Meandre Workbench with no modifications, we obtain the following output

Flow output produced by the example flow

This flow contains six instances of five different components

Instance name	Component name	Language	Description
Push String 0	Push String	Java	Push hello world
Push String 1	Push String	Java	Push hello world
Concatenate String 0	Concatenate String	Java	Concatenates two strings
To Uppercase 0	To Uppercase	Python	Converts and string to upper case
Pass Through 0	Pass Through	List	Just passes the input to the output
Print Object 0	Print Object	Java	Prints an object to the console

This flow is expressed by the following RDF descriptor

Flow RDF descriptor expressed using Turtle notation

@prefix meandre:  <http://www.meandre.org/ontology/> .
@prefix xsd:     <http://www.w3.org/2001/XMLSchema#> .
@prefix dc:      <http://purl.org/dc/elements/1.1/> .
@prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

<meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/4>
      rdf:type meandre:data_connector_configuration ;
      meandre:connector_instance_data_port_source
              <meandre://test.org/component/pass-through/output/string> ;
      meandre:connector_instance_data_port_target
              <meandre://test.org/component/print-object/input/object> ;
      meandre:connector_instance_source
              <meandre://test.org/flow/test-hello-world-with-python-and-lisp/instance/pass-through/4> ;
      meandre:connector_instance_target
              <meandre://test.org/flow/test-hello-world-with-python-and-lisp/instance/print-object/5> .

<meandre://test.org/flow/test-hello-world-with-python-and-lisp/instance/push-string/0/property/wb_top_pix_pos>
      rdf:type meandre:property ;
      meandre:key "wb_top_pix_pos"^^xsd:string ;
      meandre:value "133"^^xsd:string .

<meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/set>
      rdf:type meandre:connector_set ;
      meandre:data_connector
              <meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/4> , <meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/2> , <meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/3> , <meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/1> , <meandre://test.org/flow/test-hello-world-with-python-and-lisp/connector/0> .

...

RDF, despite all its benefits, it is not human friendly. Writing an RDF descriptor would be tedious and error prone. Thus, Meandre provides the ability to express flows in a human-friendly readable using the ZigZag scripting language. This scripting language is intended to manipulate flows without using the Workbench and to create self contained flows that can be run on standalone mode outside the Meandre server.

Converting a flow in to a ZigZag script

Meandre provides a simple tool to generate ZigZag scripts out of RDF descriptors. We can get the ZigZag script describing the flow by using the rdf2zz facility. For instance, we can generate the ZigZag script running the following command

$ java -jar rdf2zz-1.4.4.jar -i http://demo.seasr.org:1714/public/services/demo_repository.ttl -f meandre://test.org/flow/test-hello-world-with-python-and-lisp/ -o upper.zz

where http://demo.seasr.org:1714/public/services/demo_repository.ttl is the location containing the flow RDF description, and meandre://test.org/flow/test-hello-world-with-python-and-lisp/ the flow URI we want to convert to a ZigZag script. The script contained on upper.zz is listed below.

#
# Generated by RDF2ZZConverter on Wed Apr 29 10:41:16 CDT 2009
#
# @name         Hello World With Java, Python, and Lisp Components!!!
# @description  A simple hello world test
# @creator      Xavier Llor&agrave;
# @date         Tue Sep 11 21:06:03 CDT 2007
# @rights       University of Illinois/NCSA open source license
# @tags         hello_world, demo
# @uri          meandre://test.org/flow/test-hello-world-with-python-and-lisp/
#

#
# Specify component imports
#
import <http://demo.seasr.org:1714/public/services/demo_repository.ttl>

#
# Create the component aliases
#
alias <meandre://test.org/component/concatenate-strings> as CONCATENATE_STRINGS
alias <meandre://test.org/component/to-uppercase> as TO_UPPERCASE
alias <meandre://test.org/component/pass-through> as PASS_THROUGH
alias <meandre://test.org/component/push-string> as PUSH_STRING
alias <meandre://test.org/component/print-object> as PRINT_OBJECT

#
# Create the component instances
#
to_uppercasde_0 = TO_UPPERCASE()
push_string_0 = PUSH_STRING()
print_object_0 = PRINT_OBJECT()
concatenate_string_0 = CONCATENATE_STRINGS()
pass_through_0 = PASS_THROUGH()
push_string_1 = PUSH_STRING()

#
# Set component properties
#


#
# Create the flow by connecting the components
#
@to_uppercasde_0_outputs = to_uppercasde_0()
@pass_through_0_outputs = pass_through_0()
@concatenate_string_0_outputs = concatenate_string_0()
@push_string_0_outputs = push_string_0()
@push_string_1_outputs = push_string_1()

to_uppercasde_0(string: concatenate_string_0_outputs.concatenated_string)
pass_through_0(string: to_uppercasde_0_outputs.string)
concatenate_string_0(
        string_two: push_string_0_outputs.string;
        string_one: push_string_1_outputs.string
)
print_object_0(object: pass_through_0_outputs.string)

How do I create a ZigZag script from an existing flow?

Summary

A simple flow example

Converting a flow in to a ZigZag script

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