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<P>
<DIV class="title">SWI-Prolog Semantic Web Server</DIV>
<DIV class="author">Jan Wielemaker <BR>
Human Computer Studies (HCS), <BR>
University of Amsterdam <BR>
The Netherlands <BR>
E-mail: <A class="url" href="mailto:wielemak@science.uva.nl">wielemak@science.uva.nl</A></DIV>
<DIV class="abstract">
<DIV class="abstract-title">Abstract</DIV> SWI-Prolog offers an
extensive library for loading, saving and querying Semantic Web
documents. Internally, the query language is `Prolog', building on top
of an efficient implementation of a predicate <A NAME="idx:rdf3:1"></A><SPAN class="pred-ext">rdf/3</SPAN>
expressing the content of the triple store.

<P>Emerging dedicated Semantic Web query languages change this view.
Supporting such languages provides a comfortable infrastructure for
distributed Semantic Web processing systems. This document describes the
SWI-Prolog Semantic Web Server. The server provides access to the Prolog
triple store using either SeRQL or SPARQL. At the same time it is an
extensible platform for realising Semantic Web based applications.
</DIV>

<H1><A NAME="document-contents">Table of Contents</A></H1>

<DIV class="toc">
<DIV class="toc-h2"><A class="sec" href="#sec:1"><SPAN class="sec-nr">1</SPAN><SPAN class="sec-title">Introduction</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:2"><SPAN class="sec-nr">2</SPAN><SPAN class="sec-title">Query
Languages</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:2.1"><SPAN class="sec-nr">2.1</SPAN><SPAN class="sec-title">SPARQL
Support</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:2.2"><SPAN class="sec-nr">2.2</SPAN><SPAN class="sec-title">SeRQL
Support</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:3"><SPAN class="sec-nr">3</SPAN><SPAN class="sec-title">Installation
and Administration</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:3.1"><SPAN class="sec-nr">3.1</SPAN><SPAN class="sec-title">Getting
started</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:3.2"><SPAN class="sec-nr">3.2</SPAN><SPAN class="sec-title">Persistent
store</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:4"><SPAN class="sec-nr">4</SPAN><SPAN class="sec-title">Roadmap</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:4.1"><SPAN class="sec-nr">4.1</SPAN><SPAN class="sec-title">Query
processing and entailment</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:4.2"><SPAN class="sec-nr">4.2</SPAN><SPAN class="sec-title">Query
optimisation</SPAN></A></DIV>
<DIV class="toc-h3"><A class="sec" href="#sec:4.3"><SPAN class="sec-nr">4.3</SPAN><SPAN class="sec-title">Webserver</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:5"><SPAN class="sec-nr">5</SPAN><SPAN class="sec-title">The
Sesame client</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:6"><SPAN class="sec-nr">6</SPAN><SPAN class="sec-title">Sesame
interoperability</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:7"><SPAN class="sec-nr">7</SPAN><SPAN class="sec-title">The
SPARQL client</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:8"><SPAN class="sec-nr">8</SPAN><SPAN class="sec-title">Security
issues</SPAN></A></DIV>
<DIV class="toc-h2"><A class="sec" href="#sec:9"><SPAN class="sec-nr">9</SPAN><SPAN class="sec-title">Downloading</SPAN></A></DIV>
</DIV>

<P>

<H2><A NAME="sec:1"><SPAN class="sec-nr">1</SPAN><SPAN class="sec-title">Introduction</SPAN></A></H2>

<P>The SWI-Prolog Semantic Web Server unifies the SWI-Prolog general Web
support and Semantic Web support, providing both a starting point for
dedicated applications and a platform for exchange of RDF-based data
using a standardised language and protocol. An overview of the
SWI-Prolog Web support libraries can be found in <A class="url" href="http://hcs.science.uva.nl/projects/SWI-Prolog/articles/TPLP-plweb.pdf">SWI-Prolog
and the Web</A>,<SUP class="fn">1<SPAN class="fn-text">Submitted to
Theory and Practice of Logic Programming</SPAN></SUP>

<H2><A NAME="sec:2"><SPAN class="sec-nr">2</SPAN><SPAN class="sec-title">Query
Languages</SPAN></A></H2>

<P>The current server supports two query languages:
<A class="url" href="http://www.openrdf.org">SeRQL</A> and
<A class="url" href="http://www.w3.org/TR/rdf-sparql-query/">SPARQL</A>.
For both languages we provide an interactive service that presents the
results as a human-readable HTML table, a service presenting its result
as RDF/XML or XML that follows the HTTP protocol definition for the
query language, the possibility to query the local database using a
query language in Prolog and a Prolog client that can be used to query
remote services supporting the query language and HTTP service.

<P>For both query languages, queries are translated to a complex Prolog
goal calling <A NAME="idx:rdf3:2"></A><SPAN class="pred-ext">rdf/3</SPAN>
to resolve edges in the graph and calls to predicates from
rdfql_runtime.pl that realise constraints imposed by the SeRQL
<CODE>WHERE</CODE> clause and SPARQL <CODE>FILTER</CODE> clauses.

<H3><A NAME="sec:2.1"><SPAN class="sec-nr">2.1</SPAN><SPAN class="sec-title">SPARQL
Support</SPAN></A></H3>

<P>SPARQL support is based on the SPARQL specification, versioned April
6, 2006. Status:

<P><UL COMPACT>
<LI>No query optimization
<LI>Limited value-testing, notably on xsd:dateTime
<LI>Incomplete ORDER BY support. Only ascending and all values are
compared lexically.
<LI>No support for named graphs
<LI>Passes current test-suite, except tests affected by the above or
acknowledged as errornous.
</UL>

<H3><A NAME="sec:2.2"><SPAN class="sec-nr">2.2</SPAN><SPAN class="sec-title">SeRQL
Support</SPAN></A></H3>

<P>SeRQL support and compatibility is based on development version
20040820, with additional support for the new 1.2 syntax and some of the
built-in functions. Both SeRQL and the HTTP API are fully defined in the
Sesame documentation.

<H2><A NAME="sec:3"><SPAN class="sec-nr">3</SPAN><SPAN class="sec-title">Installation
and Administration</SPAN></A></H2>

<H3><A NAME="sec:3.1"><SPAN class="sec-nr">3.1</SPAN><SPAN class="sec-title">Getting
started</SPAN></A></H3>

<P>The file <CODE>parms.pl</CODE> contains a number of settings relevant
to the server. Notable the port to connect to, where to store user
information, etc. Persistent data kept by the server is a list of users
and their access rights (default <CODE>users.db</CODE>) and a file-based
backup of the in-memory store (default in the directory <CODE>SeRQL-store</CODE>).
Please check the content of <CODE>parms.pl</CODE> and follow directions
in the comments. On Unix-like systems, edit <CODE>run.pl</CODE> to
adjust the location of SWI-Prolog on the <CODE>!#</CODE> line. Next,
start <CODE>run.pl</CODE> and launch the server using the command below.

<PRE class="code">
?- serql_server.
</PRE>

<P>Now direct your browser to the server, using the default setup this
is <A class="url" href="http://localhost:3020">http://localhost:3020</A>.
If no users are defined the browser will prompt to enter the
administrative password. After that the admin and anonymous users are
created. Accounts can be created and modified by users with
administrative rights through the
<EM>List users ...</EM> link on the sidebar.

<P>To restart from scratch, stop the server, delete the users database
file and/or the triple backup file and restart the server as described
above.

<H3><A NAME="sec:3.2"><SPAN class="sec-nr">3.2</SPAN><SPAN class="sec-title">Persistent
store</SPAN></A></H3>

<A NAME="sec:backup"></A>

<P>The <CODE>parms.pl</CODE> setting <CODE>persistent_store(Directory,
Options)</CODE> can be used to specify file-based persistent backup for
the in-memory triple store. The store is a combination of quick-load
triple databases and journal files that hold the modifications made to
the triple store. Details of the persistent store are documented with
the SWI-Prolog
<A class="url" href="http://www.swi-prolog.org/packages/semweb.html">Semantic
Web package</A>

<H2><A NAME="sec:4"><SPAN class="sec-nr">4</SPAN><SPAN class="sec-title">Roadmap</SPAN></A></H2>

<H3><A NAME="sec:4.1"><SPAN class="sec-nr">4.1</SPAN><SPAN class="sec-title">Query
processing and entailment</SPAN></A></H3>

<A NAME="sec:entailment"></A>

<P>The kernel of the system is formed by <CODE>serql.pl</CODE> and <CODE>sparql</CODE>,
that implement the DCG parsers for the respective query languages as
well as a compiler that translates this into a Prolog goal executing the
query op top of the SWI-Prolog SemWeb package. The file
<CODE>rdfql_runtime.pl</CODE> contains predicates that implement the
constraints (SeRQL WHERE or SPARQL FILTER) and other constructs
generated by the query-compiler.

<P>Entailment reasoning is defined by <CODE>rdf_entailment.pl</CODE>.
Specific entailments are in seperate files:

<DL>
<DT><B><CODE>no_entailment.pl</CODE></B></DT>
<DD>
Defines entailment <CODE>none</CODE>. Query explicitely stored triples
only.</DD>
<DT><B><CODE>rdf_entailment.pl</CODE></B></DT>
<DD>
Defines entailment <CODE>rdf</CODE>. Any resource appearing in a
predicate position is of type <CODE>rdf:Property</CODE>. Any subject is
an instance of <CODE>rdf:Resource</CODE></DD>
<DT><B><CODE>rdfs_entailment.pl</CODE></B></DT>
<DD>
Defines entailment <CODE>rdfs</CODE>. Adds class- and property-hierarchy
reasoning to RDF reasoning, as well as reasoning on the basis of
property domain and range.</DD>
<DT><B><CODE>rdfslite_entailment.pl</CODE></B></DT>
<DD>
Defines entailment <CODE>rdfslite</CODE>. Only considers the class- and
property-hierarchy. Using a backward chaining solver this is much
faster, while normally keeping the intended meaning.
</DD>
</DL>

<P>The query compiler and execution system can be called directly from
Prolog.

<DL>
<DT class="pubdef"><A NAME="serql_compile/3"><STRONG>serql_compile</STRONG>(<VAR>+Query,
-Compiled, +Options</VAR>)</A></DT>
<DD class="defbody">
Compile <VAR>Query</VAR>, which is either an atom or a list of character
codes and unify <VAR>Compiled</VAR> with an opaque term representing the
query and suitable for passing to <A NAME="idx:serqlrun2:3"></A><A class="pred" href="#serql_run/2">serql_run/2</A>.
Defined
<VAR>Options</VAR> are:

<DL>
<DT><STRONG>entailment</STRONG>(<VAR>Entailment</VAR>)</DT>
<DD class="defbody">
Entailment to use. Default is <CODE>rdfs</CODE>. See <A class="sec" href="#sec:4.1">section
4.1</A>.</DD>
<DT><STRONG>type</STRONG>(<VAR>-Type</VAR>)</DT>
<DD class="defbody">
Extract the type of query compiled and generally useful information on
it. SeRQL defines the types <CODE>construct</CODE> and
<CODE>select(VarNames)</CODE>, where <VAR>VarNames</VAR> is a list of
variables appearing in the projection.</DD>
<DT><STRONG>optimise</STRONG>(<VAR>Bool</VAR>)</DT>
<DD class="defbody">
Whether or not to optimise the query. Default is defined by the setting
<CODE>optimise_query</CODE>.
</DD>
</DL>

</DD>
<DT class="pubdef"><A NAME="sparql_compile/3"><STRONG>sparql_compile</STRONG>(<VAR>+Query,
-Compiled, +Options</VAR>)</A></DT>
<DD class="defbody">
Similar to to <A NAME="idx:serqlcompile3:4"></A><A class="pred" href="#serql_compile/3">serql_compile/3</A>.
Defined types are extended with
<CODE>describe</CODE> and <CODE>ask</CODE>. Addional options are:

<DL>
<DT><STRONG>base_uri</STRONG>(<VAR>-URI</VAR>)</DT>
<DD class="defbody">
Base URI used to compile the query if not specified as part of the
query.</DD>
<DT><STRONG>ordered</STRONG>(<VAR>-Bool</VAR>)</DT>
<DD class="defbody">
Unify <VAR>Bool</VAR> with true if query contains an <CODE>ORDER BY</CODE>
clause.</DD>
<DT><STRONG>distinct</STRONG>(<VAR>-Bool</VAR>)</DT>
<DD class="defbody">
Unify <VAR>Bool</VAR> with true if query contains a <CODE>DISTINCT</CODE>
modifier.
</DD>
</DL>

</DD>
<DT class="pubdef"><A NAME="serql_run/2"><STRONG>serql_run</STRONG>(<VAR>+Compiled,
-Answer</VAR>)</A></DT>
<DD class="defbody">
Run a query compiled by <A NAME="idx:serqlcompile3:5"></A><A class="pred" href="#serql_compile/3">serql_compile/3</A>,
returning terms <CODE>row(Arg ...)</CODE> for select queries and terms <CODE>rdf(Subject,
Predicate, Object)</CODE> for construct queries. Subsequent results are
returned on backtracking.</DD>
<DT class="pubdef"><A NAME="sparql_run/2"><STRONG>sparql_run</STRONG>(<VAR>+Compiled,
-Answer</VAR>)</A></DT>
<DD class="defbody">
Similar to <A NAME="idx:serqlrun2:6"></A><A class="pred" href="#serql_run/2">serql_run/2</A>.
Queries of type <CODE>describe</CODE> return rdf-terms like <CODE>construct</CODE>.
Queries of type <CODE>ask</CODE> return either <CODE>true</CODE> or <CODE>false</CODE>.</DD>
<DT class="pubdef"><A NAME="serql_query/3"><STRONG>serql_query</STRONG>(<VAR>+Query,
-Answer, +Options</VAR>)</A></DT>
<DD class="defbody">
Utility combining of <A NAME="idx:serqlcompile3:7"></A><A class="pred" href="#serql_compile/3">serql_compile/3</A>
and <A NAME="idx:serqlrun2:8"></A><A class="pred" href="#serql_run/2">serql_run/2</A>.
Note this gives no access to the column-names.</DD>
<DT class="pubdef"><A NAME="sparql_query/3"><STRONG>sparql_query</STRONG>(<VAR>+Query,
-Answer, +Options</VAR>)</A></DT>
<DD class="defbody">
Similar to <A NAME="idx:serqlquery3:9"></A><A class="pred" href="#serql_query/3">serql_query/3</A>.
</DD>
</DL>

<H3><A NAME="sec:4.2"><SPAN class="sec-nr">4.2</SPAN><SPAN class="sec-title">Query
optimisation</SPAN></A></H3>

<P>By default, but under control of the <A NAME="idx:setting1:10"></A><SPAN class="pred-ext">setting/1</SPAN>
option
<CODE>optimise_query(Bool)</CODE>, and the option <CODE>optimise(Bool)</CODE>,
the query compiler optimises initial goal obtained from naive
translation of the query text. The optimiser is defined in <CODE>rdf_optimise.pl</CODE>.
The optimiser is described in detail in <A class="url" href="http://hcs.science.uva.nl/projects/SWI-Prolog/articles/ICLP05-SeRQL.pdf">An
optimised Semantic Web query language implementation in Prolog</A>. The
optimiser reorders goals in the generated conjunction and prepares for
independent execution of independent parts of the generated goal. With
the optimiser enabled (default), the provided order of path-expressions
on the query text is completely ignored and constraints are inserted at
the earliest possible point.

<P>The SeRQL <CODE>LIKE</CODE> operator applies to both resources and
literals, while the SWI-Prolog RDF-DB module can only handle <CODE>LIKE</CODE>
efficiently on literals. The optimiser can be made aware of this using
<CODE>WHERE label(X) LIKE "joe*"</CODE>. Taking the label informs the
optimiser that it only needs to consider literals. Likewise, equivalence
tests where one of the arguments is used as subject or predicate or has
the isResource(X) constraint tell the system it can do straight
identifier comparison rather then the much more expensive general
comparison.

<P>Query optimisation is not yet supported for SPARQL.

<H3><A NAME="sec:4.3"><SPAN class="sec-nr">4.3</SPAN><SPAN class="sec-title">Webserver</SPAN></A></H3>

<P>The webserver is realised by <CODE>server.pl</CODE>, merely loading
both components: <CODE>http_data.pl</CODE> providing the Sesame HTTP API
using the same paths and parameters and <CODE>http_user.pl</CODE>
providing a browser-friendly frontend. Error messages are still very
crude and almost all errors return a 500 server error page with a
transcription of the Prolog exception.

<P>The Sesame HTTP API deals with a large number of data formats, only
part of which are realised by the current system. This realisation is
achieved through <CODE>rdf_result</CODE>, providing an extensible API
for reading and writing in different formats. <CODE>rdf_html</CODE>,
<CODE>rdf_write</CODE> and <CODE>xml_result</CODE> provide some
implementations thereof.

<H2><A NAME="sec:5"><SPAN class="sec-nr">5</SPAN><SPAN class="sec-title">The
Sesame client</SPAN></A></H2>

<P>The file <CODE>sesame_client.pl</CODE>, created by <A class="url" href="mailto:mrmenken@cs.vu.nl">Maarten
Menken</A> provides an API to remote Sesame servers. Below is a brief
documentation of the available primitives. All predicates take an option
list. To simplify applications that communicate with a single server
defauls for the server and reposititory locations can be specified using
<A NAME="idx:setsesamedefault1:11"></A><A class="pred" href="#set_sesame_default/1">set_sesame_default/1</A>.

<DL>
<DT class="pubdef"><A NAME="set_sesame_default/1"><STRONG>set_sesame_default</STRONG>(<VAR>+DefaultOrList</VAR>)</A></DT>
<DD class="defbody">
This predicate can be used to specify defaults for the options available
to the other Sesame interface predicates. A default is a term <CODE>Option(Value)</CODE>.
If a list of such options is provided all options are set in the order
of appearance in the list. This implies options later in the list may
overrule already set options. Defined options are:

<DL>
<DT><STRONG>host</STRONG>(<VAR>Host</VAR>)</DT>
<DD class="defbody">
Hostname running the Sesame server.
</DD>
<DT><STRONG>port</STRONG>(<VAR>Port</VAR>)</DT>
<DD class="defbody">
Por the sesame server listens on.
</DD>
<DT><STRONG>path</STRONG>(<VAR>Path</VAR>)</DT>
<DD class="defbody">
Path from the root to the Sesame server. For the SWI-Prolog Sesame
client, this is normally the empty atom (<CODE>''</CODE>). For thte Java
based Sesame this is normally <CODE>'/sesame'</CODE>.
</DD>
<DT><STRONG>repository</STRONG>(<VAR>Repository</VAR>)</DT>
<DD class="defbody">
Name of the repository to connect to. See also
<A NAME="idx:sesamecurrentrepository3:12"></A><A class="pred" href="#sesame_current_repository/3">sesame_current_repository/3</A>.
</DD>
</DL>

<P>Below is a typical call to connect to a sesame server:

<PRE class="code">
...,
set_sesame_default([ host(localhost),
                     port(8080),
                     path('/sesame'),
                     repository('mem-rdfs-db')
                   ]).
</PRE>

</DD>
<DT class="pubdef"><A NAME="sesame_current_repository/3"><STRONG>sesame_current_repository</STRONG>(<VAR>-Id,
-Properties, +Options</VAR>)</A></DT>
<DD class="defbody">
Enumerate the currently available Sesame repositories. <VAR>Id</VAR> is
unified to the name of the repository. <VAR>Properties</VAR> is a list
of <CODE>Name(Value)</CODE> terms providing title and access details.
<VAR>Options</VAR> specifies the host, port and path of the server.</DD>
<DT class="pubdef"><A NAME="sesame_clear_repository/1"><STRONG>sesame_clear_repository</STRONG>(<VAR>+Options</VAR>)</A></DT>
<DD class="defbody">
Remove all content from the repository. <VAR>Options</VAR> specifies the
host, port and path of the server as well as the target repository.</DD>
<DT class="pubdef"><A NAME="sesame_login/3"><STRONG>sesame_login</STRONG>(<VAR>+User,
+Password, +Options</VAR>)</A></DT>
<DD class="defbody">
Login to a Sesame server. On success the returned cookie is stored and
transmitted with each query on the same server. <VAR>Options</VAR>
specifies the host, port and path of the server.</DD>
<DT class="pubdef"><A NAME="sesame_logout/1"><STRONG>sesame_logout</STRONG>(<VAR>+Options</VAR>)</A></DT>
<DD class="defbody">
<VAR>Options</VAR> specifies the host, port and path of the server.</DD>
<DT class="pubdef"><A NAME="sesame_graph_query/3"><STRONG>sesame_graph_query</STRONG>(<VAR>+Query,
-Triple, +Options</VAR>)</A></DT>
<DD class="defbody">
Execute <VAR>Query</VAR> on the given server and return the resulting
triples on backtracking. <VAR>Options</VAR> specifies the host, port and
path of the server as well as the target repository. The example below
extracts all type relations from the default server.

<PRE class="code">
...,
sesame_graph_query('construct * from {s} &lt;rdf:type&gt; {o}',
                   rdf(S,P,O),
                   []),
</PRE>

</DD>
<DT class="pubdef"><A NAME="sesame_table_query/3"><STRONG>sesame_table_query</STRONG>(<VAR>+Query,
-Row, +Options</VAR>)</A></DT>
<DD class="defbody">
Execute <VAR>Query</VAR> on the given server and return the resulting
rows on backtracking. Each <VAR>Row</VAR> is a term of the format
<CODE>row(Col1, Col2, ... ColN)</CODE>. <VAR>Options</VAR> specifies the
host, port and path of the server as well as the target repository.</DD>
<DT class="pubdef"><A NAME="sesame_extract_rdf/2"><STRONG>sesame_extract_rdf</STRONG>(<VAR>-Triple,
+Options</VAR>)</A></DT>
<DD class="defbody">
Extract all content from an RDF repository. In addition to the server
and repository options the following options are defined:

<DL>
<DT><STRONG>schema</STRONG>(<VAR>OnOff</VAR>)</DT>
<DD class="defbody">
Extract the schema information.
</DD>
<DT><STRONG>data</STRONG>(<VAR>OnOff</VAR>)</DT>
<DD class="defbody">
Extract the plain data
</DD>
<DT><STRONG>explicit_only</STRONG>(<VAR>OnOff</VAR>)</DT>
<DD class="defbody">
Determine whether or not entailed triples are returned. Default is <CODE>off</CODE>,
returning both explicit and inferred triples.
</DD>
</DL>

</DD>
<DT class="pubdef"><A NAME="sesame_upload_file/+File, +Options"><STRONG>sesame_upload_file</STRONG>(<VAR>+File,
+Options</VAR>)</A></DT>
<DD class="defbody">
dd the content of <VAR>File</VAR> to the repository. In addition to the
server and repository options the following options are defined:

<DL>
<DT><STRONG>data_format</STRONG>(<VAR>+Format</VAR>)</DT>
<DD class="defbody">
Format of the input file. Default is <CODE>rdfxml</CODE>.
</DD>
<DT><STRONG>base_uri</STRONG>(<VAR>+BaseURI</VAR>)</DT>
<DD class="defbody">
URI for resolving local names. Default is <CODE>foo:bar</CODE>.
</DD>
<DT><STRONG>verify_data</STRONG>(<VAR>OnOff</VAR>)</DT>
<DD class="defbody">
Do/do not verify the input. Default is <CODE>off</CODE>.
</DD>
</DL>

</DD>
<DT class="pubdef"><A NAME="sesame_assert/2"><STRONG>sesame_assert</STRONG>(<VAR>+TripleOrList,
+Options</VAR>)</A></DT>
<DD class="defbody">
Assert a single <CODE>rdf(Subject, Predicate, Object)</CODE> or a list
of such terms. In addition to the server and repository options the
following options are defined:

<DL>
<DT><STRONG>base_uri</STRONG>(<VAR>+BaseURI</VAR>)</DT>
<DD class="defbody">
URI for resolving local names. Default is <CODE>foo:bar</CODE>.
</DD>
</DL>

</DD>
<DT class="pubdef"><A NAME="sesame_retract/2"><STRONG>sesame_retract</STRONG>(<VAR>+Triple,
+Options</VAR>)</A></DT>
<DD class="defbody">
Remove a triple from the repository. Variables in Triple match all
values for that field.
</DD>
</DL>

<H2><A NAME="sec:6"><SPAN class="sec-nr">6</SPAN><SPAN class="sec-title">Sesame
interoperability</SPAN></A></H2>

<P>The SWI-Prolog SeRQL engine provides a (still incomplete) drop-in
replacement for the Sesame HTTP access protocol. Sesame's remote server
class can be used to access the SWI-Prolog SeRQL engine through the
Sesame Java API. Likewise the Prolog client realised by
<CODE>sesame_client.pl</CODE> provides a Prolog API that can be used to
access both Sesame and the SWI-Prolog SeRQL engine.

<H2><A NAME="sec:7"><SPAN class="sec-nr">7</SPAN><SPAN class="sec-title">The
SPARQL client</SPAN></A></H2>

<P>The file <CODE>sparql_client.pl</CODE> provides a client to the
SPARQL HTTP protocol. The protocol defines how a SPARQL query is asked
over HTTP and how the results are presented. It is possible to use the
SeRQL protocol on the same server to perform tasks such as modifying the
triple store.

<P>The structure of the SPARQL client API is closely based on the SeRQL
client.

<DL>
<DT class="pubdef"><A NAME="sparql_query/3"><STRONG>sparql_query</STRONG>(<VAR>+Query,
-Row, +Options</VAR>)</A></DT>
<DD class="defbody">
Run a SPARQL query on a remote server, retrieving the results one-by-one
on backtracking. <VAR>Options</VAR> provide the host, port and path of
the server. <A NAME="idx:sparqlsetserver1:13"></A><A class="pred" href="#sparql_set_server/1">sparql_set_server/1</A>
can be used to define default locations.</DD>
<DT class="pubdef"><A NAME="sparql_set_server/1"><STRONG>sparql_set_server</STRONG>(<VAR>+Options</VAR>)</A></DT>
<DD class="defbody">
List of options that act as defaults for <A NAME="idx:sparqlquery3:14"></A><A class="pred" href="#sparql_query/3">sparql_query/3</A>.
Commonly set to specify the server location. For example:

<PRE class="code">
?- sparql_set_server([ host(localhost),
                       port(3020),
                       path('/sparql/')
                     ]).
</PRE>

<P></DD>
</DL>

<H2><A NAME="sec:8"><SPAN class="sec-nr">8</SPAN><SPAN class="sec-title">Security
issues</SPAN></A></H2>

<P>HTTP Communication with the server, including usernames and
passwords, is in cleartext and therefore sensitive to sniffing. The
overall security of the server is unknown. It is advised to run the
server as user with minimal access rights, only providing write access
to the user database file.

<H2><A NAME="sec:9"><SPAN class="sec-nr">9</SPAN><SPAN class="sec-title">Downloading</SPAN></A></H2>

<P>The SWI-Prolog SeRQL engine is available from CVS using the following
commands:

<PRE class="code">
% cvs -d :pserver:pl@gollem.science.uva.nl:/usr/local/cvspl login
Password: prolog
% cvs -d :pserver:pl@gollem.science.uva.nl:/usr/local/cvspl co SeRQL
</PRE>

<P>Infrequently announces and snapshots are provided through the
<A class="url" href="http://gollem.science.uva.nl/twiki/pl/bin/view/Library/SeRQL">Prolog
Wiki</A>

<H3>Acknowledgements</H3>

<P>The SeRQL server has been realised as part of the <A class="url" href="http://www.hops-fp6.org">HOPS
project</A> and could not have been done without Sesame and feedback
from Jeen Broekstra and Maarten Menken from the Free University of
Amsterdam (VU). Adding SPARQL support has been realised as part of the
E-culture sub-project of Dutch MultiMedia project.

<H1><A NAME="document-index">Index</A></H1>

<DL>
<DT><STRONG>R</STRONG></DT>
<DD>
</DD>
<DT>rdf/3</DT>
<DD>
<A class="idx" href="#idx:rdf3:1"></A> <A class="idx" href="#idx:rdf3:2">2</A></DD>
<DT><STRONG>S</STRONG></DT>
<DD>
</DD>
<DT><A class="idx" href="#serql_compile/3">serql_compile/3</A></DT>
<DD>
<A class="idx" href="#idx:serqlcompile3:4">4.1</A> <A class="idx" href="#idx:serqlcompile3:5">4.1</A> <A class="idx" href="#idx:serqlcompile3:7">4.1</A></DD>
<DT><A class="idx" href="#serql_query/3">serql_query/3</A></DT>
<DD>
<A class="idx" href="#idx:serqlquery3:9">4.1</A></DD>
<DT><A class="idx" href="#serql_run/2">serql_run/2</A></DT>
<DD>
<A class="idx" href="#idx:serqlrun2:3">4.1</A> <A class="idx" href="#idx:serqlrun2:6">4.1</A> <A class="idx" href="#idx:serqlrun2:8">4.1</A></DD>
<DT><A class="idx" href="#sesame_assert/2">sesame_assert/2</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_clear_repository/1">sesame_clear_repository/1</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_current_repository/3">sesame_current_repository/3</A></DT>
<DD>
<A class="idx" href="#idx:sesamecurrentrepository3:12">5</A></DD>
<DT><A class="idx" href="#sesame_extract_rdf/2">sesame_extract_rdf/2</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_graph_query/3">sesame_graph_query/3</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_login/3">sesame_login/3</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_logout/1">sesame_logout/1</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_retract/2">sesame_retract/2</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_table_query/3">sesame_table_query/3</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sesame_upload_file/+File, +Options">sesame_upload_file/+File,
+Options</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#set_sesame_default/1">set_sesame_default/1</A></DT>
<DD>
<A class="idx" href="#idx:setsesamedefault1:11">5</A></DD>
<DT>setting/1</DT>
<DD>
<A class="idx" href="#idx:setting1:10">4.2</A></DD>
<DT><A class="idx" href="#sparql_compile/3">sparql_compile/3</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sparql_query/3">sparql_query/3</A></DT>
<DD>
<A class="idx" href="#idx:sparqlquery3:14">7</A></DD>
<DT><A class="idx" href="#sparql_run/2">sparql_run/2</A></DT>
<DD>
</DD>
<DT><A class="idx" href="#sparql_set_server/1">sparql_set_server/1</A></DT>
<DD>
<A class="idx" href="#idx:sparqlsetserver1:13">7</A></DD>
</DL>

</BODY></HTML>
author	Chris Cannam
date	Tue, 20 Feb 2018 14:52:02 +0000
parents	df9685986338
children