[Upd] Update web page about rdf4j update module

doc/examples/rdf4j-update/rdf4j-update.md

@@ -2,4 +2,70 @@
 
 RDF4J update example explains how to update RDF4J repository.
 
-## Introduction
+## Introduction
+
+This example contains script *rdf4j-update.sms.ttl* that contain one pipeline. It creates RDF4J repository and performs update query. For more details about script construction and execution you can see [hello-world-example](https://github.com/kbss-cvut/s-pipes/blob/main/doc/examples/hello-world/hello-world.md).
+
+## Script structure
+
+Script performs following steps:
+1) Creates RDF4J repository using `kbss:rdf4j-create-repository` module. Repository is specified by parameters `rdf4j:p-rdf4j-server-url` and `rdf4j:p-rdf4j-repository-name`. Parameter `rdf4j:p-rdf4j-ignore-if-exists` defines behavior of the module in case when defined repository already exists:
+in case if it is set to be "true", module will not do anything if repository with given ID already exists on the server.  
+
+
+    :create-repository
+        a kbss:rdf4j-create-repository ;
+        rdf4j:p-rdf4j-server-url "http://localhost:8080/rdf4j-server/" ;
+        rdf4j:p-rdf4j-repository-name "test-update" ;
+        rdf4j:p-rdf4j-ignore-if-exists "true" ;
+        sm:next :update ;
+    .
+
+2) Perform an update on repository using `a kbss:rdf4j-update` module. Repository is defined in the same way as in `:create-repository`. Update query is set by string in `sp:text` section.
+
+
+    :update
+        a kbss:rdf4j-update ;
+        sm:next :update-repository_Return ;
+        sml:updateQuery [
+            a sp:Update ;
+            sp:text """
+    DELETE {
+        <http://example.org/people/john>  <http://example.org/people/age> ?oldAge .
+    }
+    INSERT {
+        <http://example.org/people/john>  <http://example.org/people/age> ?newAge .
+    } WHERE {
+        OPTIONAL {
+        <http://example.org/people/john>  <http://example.org/people/age> ?oldAge .
+        }
+        BIND(COALESCE(?oldAge+1, 1) as ?newAge)
+    }
+            """ ;
+        ];
+        rdf4j:p-rdf4j-server-url "http://localhost:8080/rdf4j-server/" ;
+        rdf4j:p-rdf4j-repository-name "test-update" ;
+        rdfs:label "Make insert update" ;
+    .
+
+## Script execution
+
+Let's assume that SPipes web application is running at `http://localhost:8080/s-pipes`. We can call the *pipeline* with:
+
+    http://localhost:8080/s-pipes/service?_pId=update-repository
+
+Note, that rdf4j server should be running on the URL that is specified in script (`http://localhost:8080/rdf4j-server/` for example).
+You can see following logs while execution:
+
+    [http-nio-8080-exec-7] INFO  c.c.s.e.ExecutionEngineImpl -  ##### create-repository
+    ...
+    INFO [http-nio-8080-exec-7] cz.cvut.spipes.modules.Rdf4jCreateRepositoryModule.executeSelf Server url: http://localhost:8080/rdf4j-server/ Repository name: test-update Ignore flag: true
+    INFO [http-nio-8080-exec-6] cz.cvut.spipes.modules.Rdf4jCreateRepositoryModule.executeSelf Repository "test-update" already exists
+    ...
+    [http-nio-8080-exec-7] INFO  c.c.s.e.ExecutionEngineImpl -  ##### Make insert update
+    ...
+    INFO [http-nio-8080-exec-7] cz.cvut.spipes.modules.Rdf4jUpdateModule.loadConfiguration Connection created for repository test-update
+    INFO [http-nio-8080-exec-7] cz.cvut.spipes.modules.Rdf4jUpdateModule.makeUpdate Update executed
+
+This log will occur when Ignore flag is set to true and repository already exists:
+`INFO [http-nio-8080-exec-6] cz.cvut.spipes.modules.Rdf4jCreateRepositoryModule.executeSelf Repository "test-update" already exists`