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[tracker/wip/carlosg/domain-ontologies: 55/116] docs: Add documentation around creating and maintaining ontologies

commit 0b0541b4731f9a421beb7fbbdc1891b758cd6e9c
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Jun 14 18:51:42 2017 +0200

    docs: Add documentation around creating and maintaining ontologies
    
    If we now expose that detail to users, it's better to have it
    documented properly.

 .../examples/ontologies/defining-cardinality-1.rq  |    5 +
 .../examples/ontologies/defining-cardinality-2.txt |    4 +
 .../examples/ontologies/defining-cardinality-3.rq  |    8 +
 .../examples/ontologies/defining-classes-1.txt     |    3 +
 .../examples/ontologies/defining-classes-2.txt     |   11 +
 .../examples/ontologies/defining-classes-3.rq      |    2 +
 .../examples/ontologies/defining-fts-indexes-1.txt |    5 +
 .../examples/ontologies/defining-fts-indexes-2.rq  |    2 +
 .../examples/ontologies/defining-indexes-1.txt     |    5 +
 .../examples/ontologies/defining-namespaces-1.txt  |   16 +
 .../examples/ontologies/defining-properties-1.txt  |   11 +
 .../examples/ontologies/defining-properties-2.txt  |    7 +
 .../examples/ontologies/defining-properties-3.txt  |    8 +
 .../examples/ontologies/defining-properties-4.rq   |    5 +
 .../examples/ontologies/defining-uniqueness-1.txt  |    3 +
 .../examples/ontologies/defining-uniqueness-2.rq   |    7 +
 .../examples/ontologies/predefined-elements-1.txt  |    1 +
 .../examples/ontologies/predefined-elements-2.rq   |    2 +
 .../libtracker-sparql/libtracker-sparql-docs.sgml  |    1 +
 docs/reference/libtracker-sparql/ontologies.sgml   |  352 ++++++++++++++++++++
 20 files changed, 458 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-1.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-1.rq
new file mode 100644
index 0000000..326caa2
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-1.rq
@@ -0,0 +1,5 @@
+INSERT DATA { <cat> a ex:Mammal .
+              <dog> a ex:Mammal .
+
+              <peter> a ex:Mammal ;
+                    ex:pets <cat>, <dog> }
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-2.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-2.txt
new file mode 100644
index 0000000..9674e4f
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-2.txt
@@ -0,0 +1,4 @@
+ex:cromosomes a rdf:Property;
+              rdfs:domain ex:Eukaryote;
+              rdfs:range xsd:integer;
+              nrl:maxCardinality 1.
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-3.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-3.rq
new file mode 100644
index 0000000..c5502e1
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-cardinality-3.rq
@@ -0,0 +1,8 @@
+# This will fail
+INSERT DATA { <cat> a ex:Mammal;
+                    ex:cromosomes 38;
+                    ex:cromosomes 42 }
+
+# This will succeed
+INSERT DATA { <donald> a ex:Mammal;
+                       ex:cromosomes 47 }
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-1.txt
new file mode 100644
index 0000000..960de6a
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-1.txt
@@ -0,0 +1,3 @@
+ex:Eukaryote a rdfs:Class;
+             rdfs:subclassOf rdfs:Resource;
+             rdfs:comment "An eukaryote".
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-2.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-2.txt
new file mode 100644
index 0000000..5d1dc9c
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-2.txt
@@ -0,0 +1,11 @@
+ex:Animal a rdfs:Class;
+          rdfs:subclassOf ex:Eukaryote;
+          rdfs:comment "An animal".
+
+ex:Plant a rdfs:Class;
+          rdfs:subclassOf ex:Eukaryote;
+          rdfs:comment "A plant".
+
+ex:Mammal a rdfs:Class;
+          rdfs:subclassOf ex:Animal;
+          rdfs:comment "A mammal".
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-3.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-3.rq
new file mode 100644
index 0000000..c695103
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-classes-3.rq
@@ -0,0 +1,2 @@
+INSERT DATA { <merry> a ex:Mammal }
+INSERT DATA { <treebeard> a ex:Animal, ex:Plant }
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-fts-indexes-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-fts-indexes-1.txt
new file mode 100644
index 0000000..801a746
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-fts-indexes-1.txt
@@ -0,0 +1,5 @@
+ex:name a rdf:Property;
+        rdfs:domain ex:Mammal;
+        rdfs:range xsd:string;
+        tracker:fulltextIndexed true;
+        tracker:weight 10.
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-fts-indexes-2.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-fts-indexes-2.rq
new file mode 100644
index 0000000..1b13d99
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-fts-indexes-2.rq
@@ -0,0 +1,2 @@
+SELECT { ?mammal a ex:Mammal;
+                 fts:match "timmy" }
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-indexes-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-indexes-1.txt
new file mode 100644
index 0000000..462ea56
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-indexes-1.txt
@@ -0,0 +1,5 @@
+# Make queries on ex:dateOfBirth faster
+ex:Mammal a rdfs:Class;
+          rdfs:subclassOf ex:Animal;
+          rdfs:comment "A mammal";
+          tracker:domainIndex ex:dateOfBirth.
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-namespaces-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-namespaces-1.txt
new file mode 100644
index 0000000..ab00fa9
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-namespaces-1.txt
@@ -0,0 +1,16 @@
+# These prefixes will be used in the definition of the ontology,
+# thus must be explicitly defined
+@prefix nrl: <http://www.semanticdesktop.org/ontologies/2007/08/15/nrl#> .
+@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
+@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
+@prefix tracker: <http://www.tracker-project.org/ontologies/tracker#> .
+@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
+@prefix nao: <http://www.semanticdesktop.org/ontologies/2007/08/15/nao#> .
+
+# This is our example namespace
+@prefix ex: <http://example.org/#>
+
+ex: a tracker:Namespace, tracker:Ontology
+    tracker:prefix "ex"
+    rdfs:comment "example ontology"
+    nao:lastModified "2017-01-01T15:00:00Z"
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-1.txt
new file mode 100644
index 0000000..2a391f4
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-1.txt
@@ -0,0 +1,11 @@
+ex:cromosomes a rdf:Property;
+              rdfs:domain ex:Eukaryote;
+              rdfs:range xsd:integer.
+
+ex:unicellular a rdf:Property;
+               rdfs:domain ex:Eukaryote;
+               rdfs:range xsd:bool;
+
+ex:dateOfBirth a rdf:Property;
+               rdfs:domain ex:Mammal;
+               rdfs:range xsd:dateTime;
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-2.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-2.txt
new file mode 100644
index 0000000..c808a25
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-2.txt
@@ -0,0 +1,7 @@
+ex:parent a rdf:Property;
+          rdfs:domain ex:Mammal;
+          rdfs:range ex:Mammal;
+
+ex:pet a rdf:Property;
+       rdfs:domain ex:Mammal;
+       rdfs:range ex:Eukaryote;
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-3.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-3.txt
new file mode 100644
index 0000000..05f8aeb
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-3.txt
@@ -0,0 +1,8 @@
+ex:geneticInformation a rdf:Property;
+                      rdfs:domain ex:Eukaryote;
+                      rdfs:range xsd:string;
+
+ex:dna a rdf:Property;
+       rdfs:domain ex:Mammal;
+       rdfs:range xsd:string;
+       rdfs:subPropertyOf ex:geneticInformation.
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-4.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-4.rq
new file mode 100644
index 0000000..0f44af2
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-properties-4.rq
@@ -0,0 +1,5 @@
+# These two queries should provide the exact same result(s)
+SELECT { ?animal a ex:Animal;
+                 ex:geneticInformation "AGCT" }
+SELECT { ?animal a ex:Animal;
+                 ex:dna "AGCT" }
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-uniqueness-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-uniqueness-1.txt
new file mode 100644
index 0000000..14a6ed7
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-uniqueness-1.txt
@@ -0,0 +1,3 @@
+ex:geneticInformation a rdf:Property, nrl:InverseFunctionalProperty;
+                      rdfs:domain ex:Eukaryote;
+                      rdfs:range xsd:string;
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/defining-uniqueness-2.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/defining-uniqueness-2.rq
new file mode 100644
index 0000000..6459d50
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/defining-uniqueness-2.rq
@@ -0,0 +1,7 @@
+# First insertion, this will succeed
+INSERT DATA { <drosophila> a ex:Eukariote;
+                           ex:geneticInformation "AGCT" }
+
+# This will fail
+INSERT DATA { <melanogaster> a ex:Eukariote;
+                             ex:geneticInformation "AGCT" }
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/predefined-elements-1.txt 
b/docs/reference/libtracker-sparql/examples/ontologies/predefined-elements-1.txt
new file mode 100644
index 0000000..a65eb5a
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/predefined-elements-1.txt
@@ -0,0 +1 @@
+ex:self a ex:Mammal.
diff --git a/docs/reference/libtracker-sparql/examples/ontologies/predefined-elements-2.rq 
b/docs/reference/libtracker-sparql/examples/ontologies/predefined-elements-2.rq
new file mode 100644
index 0000000..552849c
--- /dev/null
+++ b/docs/reference/libtracker-sparql/examples/ontologies/predefined-elements-2.rq
@@ -0,0 +1,2 @@
+INSERT DATA { ex:self ex:pets <cat> .
+              <cat> ex:pets ex:self }
diff --git a/docs/reference/libtracker-sparql/libtracker-sparql-docs.sgml 
b/docs/reference/libtracker-sparql/libtracker-sparql-docs.sgml
index 34ac6b5..8e628ba 100644
--- a/docs/reference/libtracker-sparql/libtracker-sparql-docs.sgml
+++ b/docs/reference/libtracker-sparql/libtracker-sparql-docs.sgml
@@ -38,6 +38,7 @@
     <xi:include href="xml/tracker-version.xml"/>
   </part>
 
+  <xi:include href="ontologies.sgml"/>
   <xi:include href="examples.sgml"/>
 
   <xi:include href="xml/annotation-glossary.xml"><xi:fallback /></xi:include>
diff --git a/docs/reference/libtracker-sparql/ontologies.sgml 
b/docs/reference/libtracker-sparql/ontologies.sgml
new file mode 100644
index 0000000..615ff74
--- /dev/null
+++ b/docs/reference/libtracker-sparql/ontologies.sgml
@@ -0,0 +1,352 @@
+<?xml version='1.0' encoding="UTF-8"?>
+
+<part id="tracker-ontologies" xmlns:xi="http://www.w3.org/2003/XInclude";>
+  <title>Defining ontologies</title>
+  <partintro>
+    <para>
+      An ontology defines the entities that a Tracker endpoint can store, as
+      well as their properties and the relationships between different entities.
+    </para>
+    <para>
+      Tracker internally uses the following ontologies as its base, all ontologies
+      defined by the user of the endpoint are recommended to be build around this
+      base:
+    </para>
+
+    <formalpara>
+      <title><systemitem>XML Schema (XSD).</systemitem></title>
+      <para>Defining basic types.</para>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Resource Description Framework (RDF).</systemitem></title>
+      <para>Defining classes, properties and inheritance</para>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Nepomuk Resource Language (NRL).</systemitem></title>
+      <para>Defining resource uniqueness and cardinality</para>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Dublin Core (DC).</systemitem></title>
+      <para>Defining common superproperties for documents</para>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Nepomuk Annotation Ontology (NAO).</systemitem></title>
+      <para>Implementing tagging and annotations</para>
+    </formalpara>
+
+    <para>
+      Ontologies are RDF files with the .ontology extension, Tracker parses all
+      ontology files from the given directory. The individual ontology files may
+      ontologies may not be self-consistent (i.e. use missing definitions), but
+      all the ontology files as a whole must be.
+    </para>
+
+    <para>
+      Tracker loads the ontology files in alphanumeric order, it is advisable
+      that those have a numbered prefix in order to load those at a consistent
+      order despite future additions.
+    </para>
+  </partintro>
+
+  <chapter id="creating-ontology">
+    <title>Creating an ontology</title>
+    <section id="defining-namespaces">
+      <title>Defining a namespace</title>
+      <para>
+       A namespace is the topmost layer of an individual ontology, it will
+       contain all classes and properties defined by it. In order to define
+       a namespace you can do:
+      </para>
+      <programlisting><xi:include href="examples/ontologies/defining-namespaces-1.txt" 
parse="text"/></programlisting>
+    </section>
+    <section id="defining-classes">
+      <title>Defining classes</title>
+      <para>
+       Classes are the base of an ontology, all stored resources must define
+       themselves as "being" at least one of these classes. They all derive
+       from the base rdfs:Resource type. To eg. define classes representing
+       animals and plants, you can do:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-classes-1.txt" 
parse="text"/></programlisting>
+      <para>
+       By convention all classes use CamelCase names, although class names
+       are not restricted. The allowed charset is UTF-8.
+      </para>
+      <para>
+       Declaring subclasses is possible:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-classes-2.txt" 
parse="text"/></programlisting>
+      <para>
+       With such classes defined, resources may be inserted to the endpoint,
+       eg. with the SPARQL:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-classes-3.rq" 
parse="text"/></programlisting>
+      <para>
+       Note that multiple inheritance is possible, resources will just inherit
+       all properties from all classes and superclasses.
+      </para>
+    </section>
+    <section id="defining-properties">
+      <title>Defining properties</title>
+      <para>
+       Properties relate to a class, so all resources pertaining to that class
+       can define values for these.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-properties-1.txt" 
parse="text"/></programlisting>
+      <para>
+       The class the property belongs to is defined by rdfs:domain, while the
+       data type contained is defined by rdfs:range. By convention all
+       properties use lowerCamelCase names, although property names are not
+       restricted. The allowed charset is UTF-8.
+      </para>
+      <para>
+       The following basic types are supported:
+      </para>
+      <formalpara>
+       <title><systemitem>xsd:boolean</systemitem></title>
+      </formalpara>
+      <formalpara>
+       <title><systemitem>xsd:string</systemitem></title>
+      </formalpara>
+      <formalpara>
+       <title><systemitem>xsd:integer</systemitem></title>
+       <para>Ranging from -2^63 to 2^63-1.</para>
+      </formalpara>
+      <formalpara>
+       <title><systemitem>xsd:double</systemitem></title>
+       <para>Able to store a 8 byte IEEE floating point number.</para>
+      </formalpara>
+      <formalpara>
+       <title><systemitem>xsd:date and xsd:dateTime</systemitem></title>
+       <para>
+         Able to store dates and times since January 1, 1970 UTC, with
+         millisecond resolution.
+       </para>
+      </formalpara>
+      <para>
+       Of course, properties can also point to resources of the same or
+       other classes, so stored resources can conform a graph:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-properties-2.txt" 
parse="text"/></programlisting>
+      <para>
+       There is also inheritance of properties, an example would be a property
+       in a subclass concretizing a more generic property from a superclass.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-properties-3.txt" 
parse="text"/></programlisting>
+      <para>
+       SPARQL queries are expected to provide the same result when queried
+       for a property or one of its superproperties.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-properties-4.rq" 
parse="text"/></programlisting>
+    </section>
+    <section id="defining-cardinality">
+      <title>Defining cardinality of properties</title>
+      <para>
+       By default, properties are multivalued, there are no restrictions in
+       the number of values a property can store.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-cardinality-1.rq" 
parse="text"/></programlisting>
+      <para>
+       Wherever this is not desirable, cardinality can be limited on properties
+       through nrl:maxCardinality.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-cardinality-2.txt" 
parse="text"/></programlisting>
+      <para>
+       This will raise an error if the SPARQL updates in the endpoint end up
+       in the property inserted multiple times.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-cardinality-3.rq" 
parse="text"/></programlisting>
+      <note>
+       Tracker does not implement support for other maximum cardinalities
+       than 1.
+      </note>
+      <!--
+         XXX: explain how cardinality affects subproperties, superproperties
+       -->
+    </section>
+    <section id="defining-uniqueness">
+      <title>Defining uniqueness</title>
+      <para>
+       It is desirable for certain properties to keep their values unique
+       across all resources, this can be expressed by defining the properties
+       as being a nrl:InverseFunctionalProperty.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-uniqueness-1.txt" 
parse="text"/></programlisting>
+      <para>
+       With that in place, no two resources can have the same value on the
+       property.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-uniqueness-2.rq" 
parse="text"/></programlisting>
+      <!--
+         XXX: explain how inverse functional proeprties affect sub/superproperties
+       -->
+    </section>
+    <section id="defining-indexes">
+      <title>Defining indexes</title>
+      <para>
+       It may be the case that SPARQL queries performed on the endpoint are
+       known to match, sort, or filter on certain properties more often than others.
+       In this case, the ontology may use tracker:domainIndex in the class definition:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-indexes-1.txt" 
parse="text"/></programlisting>
+      <para>
+       Classes may define multiple domain indexes.
+      </para>
+      <note>
+       Be frugal with indexes, do not add these proactively. An index in the wrong
+       place might not affect query performance positively, but all indexes come at
+       a cost in disk size.
+      </note>
+    </section>
+    <section id="defining-fts-indexes">
+      <title>Defining full-text search properties</title>
+      <para>
+       Tracker provides nonstandard full-text search capabilities, in order to use
+       these, the string properties can use tracker:fulltextIndexed:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-fts-indexes-1.txt" 
parse="text"/></programlisting>
+      <para>
+       Weighting can also be applied, so certain properties rank higher than others
+       in full-text search queries. With tracker:fulltextIndexed in place, sparql
+       queries may use full-text search capabilities:
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/defining-fts-indexes-2.rq" 
parse="text"/></programlisting>
+    </section>
+    <section id="predefined-elements">
+      <title>Predefined elements</title>
+      <para>
+       It may be desirable for the ontology to offer predefined elements of a
+       certain class, which can then be used by the endpoint.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/predefined-elements-1.txt" 
parse="text"/></programlisting>
+      <para>
+       Usage does not differ in use from the elements of that same class that
+       could be inserted in the endpoint.
+      </para>
+      <programlisting><xi:include href="./examples/ontologies/predefined-elements-2.rq" 
parse="text"/></programlisting>
+    </section>
+  </chapter>
+
+  <chapter id="accompanying-metadata">
+    <title>Accompanying metadata</title>
+    <para>
+      Ontology files are optionally accompanied by description files, those have
+      the same basename, but the ".description" extension.
+    </para>
+    <programlisting><xi:include href="./examples/ontologies/example.description" 
parse="text"/></programlisting>
+  </chapter>
+
+  <chapter id="updating-ontology">
+    <title>Updating an ontology</title>
+
+    <para>
+      As software evolves, sometimes changes in the ontology are unavoidable.
+      Tracker can transparently handle certain ontology changes on existing
+      databases.
+    </para>
+
+    <formalpara>
+      <title><systemitem>Adding a class.</systemitem></title>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Removing a class.</systemitem></title>
+      <para>
+       All resources will be removed from this class, and all related
+       properties will disappear.
+      </para>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Adding a property.</systemitem></title>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Removing a property.</systemitem></title>
+      <para>
+       The property will disappear from all elements pertaining to the
+       class in domain of the property.
+      </para>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Changing rdfs:range of a property.</systemitem></title>
+      <para>
+       The following conversions are allowed:
+      </para>
+      <variablelist>
+       <varlistentry><listitem>xsd:integer to xsd:bool, xsd:double and xsd:string</listitem></varlistentry>
+       <varlistentry><listitem>xsd:double to xsd:bool, xsd:integer and xsd:string</listitem></varlistentry>
+       <varlistentry><listitem>xsd:string to xsd:bool, xsd:integer and xsd:double</listitem></varlistentry>
+      </variablelist>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Adding and removing tracker:domainIndex from a class.</systemitem></title>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Adding and removing tracker:fulltextIndexed from a property.</systemitem></title>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Changing the tracker:weight on a property.</systemitem></title>
+    </formalpara>
+    <formalpara>
+      <title><systemitem>Removing nrl:maxCardinality from a property.</systemitem></title>
+    </formalpara>
+    <!--
+       XXX: these need documenting too
+       add intermediate superproperties
+       add intermediate superclasses
+       remove intermediate superproperties
+       remove intermediate superclasses
+      -->
+
+    <para>
+      However, there are certain ontology changes that Tracker will find
+      incompatible. Either because they are incoherent or resulting into
+      situations where it can not deterministically satisfy the change
+      in the stored data. Tracker will error out and refuse to do any data
+      changes in these situations:
+    </para>
+    <variablelist>
+      <varlistentry><listitem>
+       Properties with rdfs:range being xsd:bool, xsd:date, xsd:dateTime,
+       or any other custom class are not convertible. Only conversions
+       covered in the list above are accepted.
+      </listitem></varlistentry>
+      <varlistentry><listitem>
+       You can not add rdfs:subClassOf in classes that are not being
+       newly added. You can not remove rdfs:subClassOf from classes.
+       The only allowed change to rdfs:subClassOf is to correct
+       subclasses when deleting a class, so they point a common
+       superclass.
+      </listitem></varlistentry>
+      <varlistentry><listitem>
+       You can not add rdfs:subPropertyOf to properties that are not
+       being newly added. You can not change an existing
+       rdfs:subPropertyOf unless it is made to point to a common
+       superproperty. You can however remove rdfs:subPropertyOf from
+       non-new properties.
+      </listitem></varlistentry>
+      <varlistentry><listitem>
+       Properties can not move across classes, thus any change in
+       rdfs:domain forbidden.
+      </listitem></varlistentry>
+      <varlistentry><listitem>
+       You can not add nrl:maxCardinality restrictions on properties that
+       are not being newly added.
+      </listitem></varlistentry>
+      <varlistentry><listitem>
+       You can not add nor remove nrl:InverseFunctionalProperty from a
+       property that is not being newly added.
+      </listitem></varlistentry>
+    </variablelist>
+    <para>
+      The recommendation to bypass these situations is the same for all,
+      use different property and class names and use SPARQL to manually
+      migrate the old data to the new format if necessary.
+    </para>
+    <para>
+      High level code is in a better position to solve the
+      possible incoherences (e.g. picking a single value if a property
+      changes from multiple values to single value). After the manual
+      data migration has been completed, the old classes and properties
+      can be dropped.
+    </para>
+  </chapter>
+</part>
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