1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
|
<?xml version="1.0" encoding="ISO-8859-1"?>
<!--
-
- This file is part of the OpenLink Software Virtuoso Open-Source (VOS)
- project.
-
- Copyright (C) 1998-2024 OpenLink Software
-
- This project is free software; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by the
- Free Software Foundation; only version 2 of the License, dated June 1991.
-
- This program is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- General Public License for more details.
-
- You should have received a copy of the GNU General Public License along
- with this program; if not, write to the Free Software Foundation, Inc.,
- 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
-
-
-->
<refentry id="RD-S-2">
<refmeta>
<refentrytitle>RDF Cartridges (RDF Mappers or RDFizers)</refentrytitle>
<refmiscinfo>tutorial</refmiscinfo>
</refmeta>
<refnamediv>
<refname>RDF Cartridges</refname>
<refpurpose>This article explains how to implement a Python based RDFa Cartridge based on pyRDFa library.</refpurpose>
</refnamediv>
<refsect1 id="RD-S-2a">
<title>Setting up server</title>
<para>
This tutorial explain steps to use the Python language to extend the Virtuoso Sponger.
</para>
<para>
The server must have installed latest Python hosting plugin. When it is installed and registered in the configuration file
a new function python_exec will be available for developers.
</para>
<para>
Setup the Virtuoso server INI to include python module
</para>
<programlisting><![CDATA[
[Plugins]
LoadPath = ../lib
Load1 = Hosting, hosting_python.so
...
]]></programlisting>
<para>
The python_exec takes following arguments:
</para>
<itemizedlist mark="bullet">
<listitem>
code - a string containing the Python code
</listitem>
<listitem>
function_name - a string containing the name of Python function to be executed
</listitem>
<listitem>
param1 : a string containing first parameter
</listitem>
<listitem>
param2 : a string containing second parameter
</listitem>
<listitem>
as many parameters as Python function has
</listitem>
</itemizedlist>
<para>
The Python based function must return a single string value.
</para>
</refsect1>
<refsect1 id="RD-S-2b">
<title>Setting up environment</title>
<para>
Before to write cartridge you need to setup Python environment. To do this you need to download and install rdflib, pyRDFa.
Read the pyRDFa paper for what additional libraries are needed.
</para>
<para>
If your Python installation have Zope support, you should disable the zope interfaces in rdflib. This is needed because Python C-API expirence problems when using sub modules within C code. In order to disable you can comment out following lines in [rdflib_home]/rdflib/__init__.py :
</para>
<programlisting><![CDATA[
36 #from rdflib.interfaces import IIdentifier, classImplements
37 #classImplements(URIRef, IIdentifier)
38 #classImplements(BNode, IIdentifier)
39 #classImplements(Literal, IIdentifier)
]]></programlisting>
<para>then do:</para>
<programlisting><![CDATA[
perl setup.py build
perl setup.py --user install
]]></programlisting>
</refsect1>
<refsect1 id="RD-S-2c">
<title>RDF Cartridge implementation notes</title>
<para>
The implementation consist of two steps:
</para>
<itemizedlist mark="bullet">
<listitem>
Make a copy of the localRDFa.py and use as template to run pyRDFa extractor over single string stream.
The details can be seen in source of pyRDFa.py code attached to this tutorial.
</listitem>
<listitem>
Make a Virtuoso/PL based stored procedure to call the Pyhton based extractor. The source of this function can be seen in rdf_cartridge.sql script.
</listitem>
</itemizedlist>
<para>
The stored procedure is used to do two main operations: to call 'processString' Python function inside pyRDFa.py script and to load the result in the Virtuoso RDF store.
</para>
<para>
Another important item is to register the cartridge with Sponger. this is done by insert statement into DB.DBA.SYS_RDF_MAPPERS table.
Note that in this example the new cartridge will be disabled if you run that code, if you want to enable and test the cartridge the flag in RM_ENABLED column must be 1. or enable the crtridge via conductor.
</para>
</refsect1>
</refentry>
|
