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/*! \page xml_loader XML file loader

\section toc Table of contents

  - \ref loader_intro
  - \ref loader_programming
  - \ref loader_use
  - \ref loader_file


\section loader_intro Introduction

The yacs loader is a class that can be used to load a calculation schema
in memory by reading and parsing a XML file describing it.

\section loader_programming Programming with the yacs loader class

To use the yacs loader class, first create a specific runtime (here a Salome one).

Then you can create an instance of the yacsloader class and call
the load method with the name of the XML file as argument.

The call to the method will return a calculation schema (instance of the Proc class).

\code
#include "RuntimeSALOME.hxx"
#include "parser.hxx"

YACS::ENGINE::RuntimeSALOME::setRuntime();
YACS::YACSLoader loader;

YACS::ENGINE::Proc* p=loader.load("file.xml");

\endcode

You can then dump to a file a graphviz diagram by calling the writeDot
method on the schema.

\code
#include <fstream>

std::ofstream f("proc.dot");
p->writeDot(f);
f.close();
\endcode

You can display the diagram with: dot -Tpng proc.dot |display.

And then execute the schema with an Executor.

\code
#include "Executor.hxx"

YACS::ENGINE::Executor executor;
executor.RunW(p);
\endcode

\section loader_use Using the yacs driver

The driver program is a program that loads a schema file and executes it
until its end. It is possible to display the schema state during the 
execution by specifying the --display option. An exemple of use is:

\code
driver --display=1 schema.xml
\endcode

Internally, it uses the loader class, the Salome runtime, the standard 
executor with all is necessary to catch exceptions.

\section loader_file Writing a XML file

To write a XML file describing a calculation schema, you need to define
several objects that are listed here :

  - the calculation schema
  - data types
  - elementary calculation nodes
  - connections between nodes
  - initialization parameters
  - composed calculation nodes


\subsection loader_schema Defining calculation schema
To define a calculation schema, simply open a proc tag
\code
<proc>
</proc>
\endcode

All following definitions must be put betwween these tags.

\subsection loader_types Defining data types
A calculation schema is composed of interconnected calculation nodes.
These nodes exchange data through data ports (in and out). The first
thing you need to do is to define all types that can be exchanged
in the schema. 

Some types are already defined by the runtime you use. For example, the
Salome runtime defines : int, double, string and bool types. It can also
define all types used by the declared components. At the moment, the
Salome runtime knows nothing about the types used by the declared components
so it is mandatory to define all data types except the four basic ones.

It is possible to define three kind of types : basic, sequence and objref.

A basic type is an atomic one so it can only be int, double, string and bool.
They are already defined so what can be defined is only alias to these types.

A definition of an alias to the double data type :
\code
<type name="mydble" kind="double"/>
\endcode

A sequence type is a constructed type that is built on already existing
types. A sequence type defines a list of elements. The definition
gives the name of the type and the type of the elements of the sequence.

To define a sequence of double type, add :
\code
<sequence name="myseqdble" content="double"/>
\endcode

All attributes in the sequence tag are mandatory.

You can then define a sequence of sequence by :
\code
<sequence name="myseqseqdble" content="myseqdble"/>
\endcode

An objref data type is an equivalent of a class in object languages.
Salome components use objects which have types such as Mesh, Field, ...
All these types can be related by inheritance relations.

Defining a base objref :
\code
<objref name="mesh"/>
\endcode

Defining a derived objref from mesh :
\code
<objref name="refinedmesh">
  <base>mesh</base>
</objref>
\endcode

It is possible to derive an objref from multiple base objref and objref names
can use name spaces. Just use a / as separator.
\code
<objref name="myns/mesh"/>
\endcode
It is useful for Salome components because objref must be mapped to 
CORBA types which can use name spaces.

Finally, it is possible to define a sequence of objref :
\code
<sequence name="myseqmesh" content="refinedmesh"/>
\endcode

\b RESTRICTION : struct type is not supported

\subsection loader_nodes Defining elementary calculation nodes
The next step is to define calculation nodes : service nodes or inline
nodes.

There are three kinds of inline nodes : script inline node, function
inline node and clone inline node, 
and three kinds of service nodes : component service node, reference
service node and node service node. 

The definition of all these nodes is described below.

- Script inline node

This kind of node corresponds to the execution of a python script with input
and output parameters. Input and output parameters are passed to the 
script through data ports.
A very simple example of an script inline node is :
\code
    <inline name="node1" >
      <script>
        <code>p1=10</code>
      </script>
      <outport name="p1" type="int"/>
    </inline>
\endcode

The inline node has a mandatory name as all kind of nodes.
The script tag indicates that it is a script inline node.
The python script appears in as much lines as necessary between code tags in the script
section.
If your script contains a lot of "<" or "&" characters - as program code often does - 
the XML element can be defined as a CDATA section.
A CDATA section starts with "<![CDATA[" and ends with "]]>":

In the example above the script calculates p1 that is an output parameter.
An output data port must then be defined. A output data port is defined
in an outport tag with two mandatory attributes : name and type that references
an already defined data type.
To define an input data port use the inport tag in place of outport.

Example of an inline node with input and output arguments :
\code
    <inline name="node1" >
      <script>
        <code>p1=p1+10</code>
      </script>
      <inport name="p1" type="int"/>
      <outport name="p1" type="int"/>
    </inline>
\endcode
Now the calculation node receives p1 as an input argument adds 10 to it
and sends it as an output argument.

- Function inline node

This kind of node corresponds to the execution of a python function with input
and output parameters. Input and output parameters are passed to the 
script through data ports.
The main difference with the script node is the execution part. The definition
of input and output ports is unchanged. In the execution part use the function
tag in place of the script tag and add a name (mandatory) which must be the same
as that of the function.

An example of an function inline node is :
\code
    <inline name="node1" >
      <function name="f">
        <code>def f(p1):</code>
        <code>  p1=p1+10</code>
        <code>  return p1</code>
      </script>
      <inport name="p1" type="int"/>
      <outport name="p1" type="int"/>
    </inline>
\endcode

- Clone inline node

This node is a convenience node to avoid repeating an inline definion.
It allows to create an inline calculation by using the definition
of another inline node. Such a kind of node is defined in a node tag
with two mandatory attributes : name (the node name) and type that indicates the name
of the already existing inline node to use for the definition. Example :

\code
  <node name="node2" type="node1"/>
\endcode

- Reference service node

A service node corresponds to the execution of a service available from a 
calculation server. It can thought of as the execution of an object method.
A service node is defined in a service tag in place of the inline tag for
the inline node.

In a reference service node the calculation server is known by its address (which
is a string meaningful for the runtime) and is supposed to exists
before executing the calculation schema. The service is known by its name.
Then the service has input and output arguments that are passed through ports
in the same way as the inline nodes.
The server address is defined as a string in a ref tag and the service name is 
defined in a method tag.
Example :
\code
    <service name="node4" >
        <ref>corbaname:rir:#test.my_context/Echo.Object</ref>
        <method>echoDouble</method>
        <inport name="p1" type="double"/>
        <outport name="p1" type="double"/>
    </service>
\endcode

The service node node4 is a reference service node because it has a ref
section. The address of the calculation server to use is a CORBA address
that must be meaningful to the runtime. The service to use is the
CORBA operation echoDouble that just gets the input and returns it.

- Component service node

This kind of node is similar to the previous one but the server does not
exist before the beginning of the execution. It's the runtime that is in charge 
of loading the calculation server or component for Salome platform.
Instead of defining the address of the server we give the name of the
component that will be loaded through the runtime by the platform.
This name is given in a component tag in place of the ref tag.
Example :
\code
    <service name="node4" >
        <component>ECHO</component>
        <method>echoDouble</method>
        <inport name="p1" type="double"/>
        <outport name="p1" type="double"/>
    </service>
\endcode

- Node service node

It's a special node that gives the possibility to create a service node that calls
a service of an already loaded component. To define such a node you need to 
indicate the name of an already existing component service node in a node tag
in place of the previous component tag.

A short example is better than a long speech :
\code
    <service name="node5" >
        <node>node4</node>
        <method>echoString</method>
        <inport name="p1" type="string"/>
        <outport name="p1" type="string"/>
    </service>
\endcode
Here, node5 is a service node that executes the echoString service of the
component that has been loaded by the component service node node4.

\subsection loader_connections Defining connections between nodes
After having defined all the calculation nodes needed, it is necessary 
to connect them to define the order of execution (control flow)
 and the exchanges of data (data flow).

- Control flow

The order of execution is defined by means of control links between
nodes.
These links are defined in a control tag with subtags fromnode and tonode
which give the names of precedent node and following node.
Example of control link :
\code
  <control> 
    <fromnode>node1</fromnode> 
    <tonode>node2</tonode> 
  </control>
\endcode
This control link indicates that execution of node2 must be after complete
execution of node1.

- Data flow

Exchange of data between nodes is defined by means of data links between 
output ports and input ports.
These links are defined in a datalink tag with subtags fromnode, tonode, fromport
and toport. The output port is specified with the node name and the output port
name. It's similar for the input port.

Example of data link :
\code
  <datalink> 
    <fromnode>node1</fromnode> <fromport>p1</fromport>
    <tonode>node2</tonode> <toport>p1</toport>
  </datalink>
\endcode
This data link indicates that the output argument p1 of node node1
will be sent to node node2 and used as input argument p1.
By default, with this datalink definition, a control link is automatically defined between node1 and node2,
to ensure a complete execution of node1 before node2 starts.
Sometimes, this control link must not be created, for instance with loops (see below).
With most simple cases, yacs loader is able to decide to create or not the control link. It is always
possible to ask explicitely a data link without control link:
\code
  <datalink control="false"> 
    <fromnode>node1</fromnode> <fromport>p1</fromport>
    <tonode>node2</tonode> <toport>p1</toport>
  </datalink>
\endcode

So, it is equivalent to write:
\code
  <datalink> 
    <fromnode>node1</fromnode> <fromport>p1</fromport>
    <tonode>node2</tonode> <toport>p1</toport>
  </datalink>
\endcode
Or:
\code
  <control> 
    <fromnode>node1</fromnode> 
    <tonode>node2</tonode> 
  </control>
  <datalink control="false"> 
    <fromnode>node1</fromnode> <fromport>p1</fromport>
    <tonode>node2</tonode> <toport>p1</toport>
  </datalink>
\endcode
Control links may be defined implicitely several times without problem.

\subsection loader_parameters Defining initialization parameters
It is possible to initialize directly input ports with constants.
This is done with a definition put in a parameter tag with subtags tonode,
toport and value.
tonode is the name of the node and toport the name of the port to initialize.
value gives the constant to use to initialize the port. This constant is 
given in XML-RPC coding convention (http://www.xmlrpc.com/).

Example of parameter initialization :
\code
    <parameter>
        <tonode>node1</tonode> <toport>p1</toport>
        <value><string>coucou</string></value>
    </parameter>
\endcode


This parameter initialization indicates that the input argument p1
of node1 is initialized with a string constant ("coucou").

\subsection loader_example1 Putting all this together
Now that we are able to define data types, calculation nodes and links, we
can define a complete calculation schema with interconnected calculation.

\code
  <proc>
    <inline name="node1" >
      <script>
        <code>p1=p1+10</code>
      </script>
      <inport name="p1" type="int"/>
      <outport name="p1" type="int"/>
    </inline>
    <inline name="node2" >
      <script>
        <code>p1=2*p1</code>
      </script>
      <inport name="p1" type="int"/>
      <outport name="p1" type="int"/>
    </inline>
    <service name="node4" >
        <ref>corbaname:rir:#test.my_context/Echo.Object</ref>
        <method>echoDouble</method>
        <inport name="p1" type="double"/>
        <outport name="p1" type="double"/>
    </service>
    <control> 
      <fromnode>node1</fromnode> <tonode>node2</tonode> 
    </control>
    <control> 
      <fromnode>node1</fromnode> <tonode>node4</tonode> 
    </control>
    <datalink> 
      <fromnode>node1</fromnode> <fromport>p1</fromport>
      <tonode>node2</tonode> <toport>p1</toport>
    </datalink>
    <datalink> 
      <fromnode>node1</fromnode> <fromport>p1</fromport>
      <tonode>node4</tonode> <toport>p1</toport>
    </datalink>
    <parameter>
      <tonode>node1</tonode> <toport>p1</toport>
      <value><int>5</int></value>
    </parameter>
  </proc>
\endcode
We have put together 2 inline nodes and one reference service node
with nodes node2 and node4 that will be concurrently executed as can
be seen on the control flow diagram below.

\image html schema.jpeg

\subsection loader_composed Defining composed calculation nodes
The next step is to define composed nodes either to modularize the calculation
schema or to introduce control nodes like loop or switch.

- Using block to modularize the schema

All the previously defined elements (except the data types) can be put
in block nodes. It is easy : create a bloc tag with an attribute name
that contains all the definitions and you have a composed node that is
a block.

Example of block :
\code
<bloc name="b">
    <inline name="node1" >
      <script>
        <code>p1=p1+10</code>
      </script>
      <inport name="p1" type="int"/>
      <outport name="p1" type="int"/>
    </inline>
    <service name="node4" >
        <ref>corbaname:rir:#test.my_context/Echo.Object</ref>
        <method>echoDouble</method>
        <inport name="p1" type="double"/>
        <outport name="p1" type="double"/>
    </service>
    <control> 
      <fromnode>node1</fromnode> <tonode>node4</tonode> 
    </control>
    <datalink> 
      <fromnode>node1</fromnode> <fromport>p1</fromport>
      <tonode>node4</tonode> <toport>p1</toport>
    </datalink>
</bloc>
\endcode
This block can now be linked with other nodes of any kind in the same way
as elementary nodes.
The rules are : it is not possible to set control links that cross the boundary
of the block. On the other end, it is possible to set data links that cross
this boundary either on input or on output.

- Defining a For Loop

If you want to execute a calculation n times, you can use a ForLoop node
to define this kind of computation.
A for loop is defined in a forloop tag that has 2 attributes : name and nsteps.
name is as always the name of the node and nsteps is the number of steps of the 
loop. The for loop must contain one and only one node that can be an elementary
calculation node or a composed node. It is possible to have a for loop in a for loop, for 
example. If you want to put more than one calculation node in a for loop, use
a block.

Example :
\code
    <forloop name="l1" nsteps="5">
      <inline name="node2" >
        <script>
          <code>p1=p1+10</code>
        </script>
        <inport name="p1" type="int"/>
        <outport name="p1" type="int"/>
      </inline>
    </forloop >
\endcode
The rules are the same as for the block node. But inside loops, to be able to perform 
iterative computation, it is allowed to link an output port of an internal node 
with an input port of a previous node in control flow. The only limitation is that
you have to put the node and the data link in a block node as links can't be defined
in a forloop section.

Here is an example :
\code
  <forloop name="l1" nsteps="5">
    <bloc name="b">
      <inline name="node2" >
        <script>
          <code>p1=p1+10</code>
        </script>
        <inport name="p1" type="int"/>
        <outport name="p1" type="int"/>
      </inline>
      <datalink control="false">
        <fromnode>node2</fromnode> <fromport>p1</fromport>
        <tonode>node2</tonode> <toport>p1</toport>
      </datalink>
    </bloc>
  </forloop >
\endcode

Last point : it is possible to link the nsteps entry of the for loop
with an output port that produces integer data. The input port
of the loop has the same name as the attribute (nsteps).

- Defining a While Loop

This kind of loop is mainly similar to the for loop. The only difference is that
the loop executes as long as a condition is true. A while loop is defined in
a whileloop tag and has only one attribute : name as usual.
The condition value is set through an input port (which name is condition) 
that accepts boolean value.

Example of a while loop:
\code
  <whileloop name="l1" >
    <bloc name="b">
      <inline name="node2" >
        <script>
          <code>p1=p1+10</code>
          <code><![CDATA[  condition=p1 < 40.]]> </code>
        </script>
        <inport name="p1" type="int"/>
        <outport name="p1" type="int"/>
        <outport name="condition" type="bool"/>
      </inline>
      <datalink control="false">
        <fromnode>node2</fromnode> <fromport>p1</fromport>
        <tonode>node2</tonode> <toport>p1</toport>
      </datalink>
    </bloc>
  </whileloop >
  <datalink control="false">
    <fromnode>l1.b.node2</fromnode> <fromport>condition</fromport>
    <tonode>l1</tonode> <toport>condition</toport>
  </datalink>
  <parameter>
    <tonode>l1.b.node2</tonode> <toport>p1</toport>
    <value><int>23</int> </value>
  </parameter>
\endcode

It is here again possible to define composed node of any kind as internal
node to define loops in loops.

- Defining a Switch Loop

A switch node is equivalent to a switch C. It has an input port (which name
is select) that accepts integer data. According to the value in the select 
port one or another case node is selected for execution. Each case is defined
in a case tag with one attribute id that must be an integer or default. If no case
is defined for the select value the switch node uses the default case.
A case can contain one and only one internal node.

A minimal but almost complete example :
\code
    <inline name="n" >
        <script>
            <code>select=3</code>
        </script>
        <outport name="select" type="int"/>
    </inline>

    <switch name="b1">
      <case id="3">
        <inline name="n2" >
          <script><code>print p1</code></script>
          <inport name="p1" type="double"/>
          <outport name="p1" type="double"/>
        </inline>
      </case>
      <default>
        <inline name="n2" >
          <script><code>print p1</code></script>
          <inport name="p1" type="double"/>
          <outport name="p1" type="double"/>
        </inline>
      </default>
    </switch>

    <control> <fromnode>n</fromnode> <tonode>b1</tonode> </control>
    <datalink> <fromnode>n</fromnode><fromport>select</fromport>
               <tonode>b1</tonode> <toport>select</toport> </datalink>
    <parameter>
        <tonode>b1.3.n2</tonode> <toport>p1</toport>
        <value><double>54</double> </value>
    </parameter>
    <parameter>
        <tonode>b1.default.n2</tonode> <toport>p1</toport>
        <value><double>54</double> </value>
    </parameter>
\endcode


*/