ShEx/CurrentDiscussion

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Current Discussion and work

Discussion 1, redefining and including other SHEX definitions

The RELAX NG compact syntax allows for including other definitions and it allows for redefining element in existing definitions. I think it would be nice if SHEX would support something similar.

Redefining rules

In the following example a property is been redefined twice

ex:Person
{
  ex:age xsd:int,
  foaf:friend @xsd:Person* 
}
ex:PetLover & ex:Person
{
  foaf:friend @xsd:Pet*
} 

With the current implementation a redefinition means that both rules must be satisfied, which is good.

However, in some cases you would like to either

  1. indicate is that is either should apply to the first or the new rule (what we want in this example)
  2. redefine the rule completely
  3. remove the rule

This would look like

ex:Person
{
  ex:age xsd:int,
  foaf:friend @xsd:Person* 
}
ex:PetLover & ex:Person
{
  |= foaf:friend @xsd:Pet* #define or relation ship with the other rule properties
  = foaf:friend @xsd:Pet* #completely redefine the rule property
  - foaf:friend #remove the rule property
}

Inclusion

One SHEX file should be able to include another one if defined within a namespace. This could look something like

SHEX ex:persons #define namespace which can then be extended
{
  ex:Person
  {
    ex:age xsd:string,
    foaf:friend @xsd:Person* 
  }
}

included by the a second namespace

@include persons1.sh #include file and load all namespaces specified in these file
SHEX ex:personsv2 
{
  use ex:persons #use namespace ex:persons 
  ex:Person
  {(ex:age xsd:string | ex:age xsd:int)?,       
    = ex:age xsd:int
  }
}

named groups

To be able to update/redefine subgroup they should be named. Being able to name them and define separately without them to be directly a Resource Shape would solve the problem of having an higher expressive power in the RDF serialization format than in the SHEX language definition. See RDF_serialization Overview and discussion.

This would look something like

#defining an or rule which is not a ResourceShape and can not be referenced by a ShapeProperty, but can be used within an ruleGroup or ResourceShape
SHEX ex:persons
{
  @someOrRule { 
    prop1 xsd:string,
    prop2 xsd:string
  }
 
  ex:Person & someOrRule
  {
    @ageOrGroup(ex:age xsd:string | ex:age xsd:int)?,  
  }
}

Which can be the redefined with something like

SHEX ex:persons2
{
  use ex:persons
  @ageOrGroup {
    =ex:age xsd:int #redefine the age property to int and remove the optional
  }
}

Discussion 2, occurs, multiplicity and reverse multiplicity

Currently(28-2-2017) SHEX support the definition of forward as well as reverse multiplicity as it is also possible in UML.

ex:Person {
  ex:friends @ex:Person* #A person can have multiple friends 
  ^ex:friends @ex:Person* #A person can be friend of multiple persons (reverse multiplicity)
  ex:spous @ex:Person #Person can only have one lover 
  ^ex:spous @ex:Person #Person can only once Persons spous
  ex:owns ex:Car* #A Person may own multiple cars
}
ex:Car {
  ex:brand xsd:String 
  ^ex:owns ex:Car* #A car can only have one owner
}

However, defining the reverse multiplicity is quiet cumbersome and would look nicer if it would be defined like as

ex:Person {
  ex:friends @ex:Person*-* #Set forward and reverse multiplicity at once 0:N <-> 0:N
  ex:spous @ex:Person1-1  #Set forward and reverse multiplicity at once 1:1 <-> 1:1
  ex:owns ex:Car*-1  #Set forward and reverse multiplicity at once 1:N <-> 1:N
}
ex:Car {
  ex:brand xsd:String 
}

Discussion 3, enumeration values, full class support

In my opinion it would be nice not to only support simple enumeration ranges like:

<IssueShape>
{
  ex:state      [ex:unassigned ex:assigned]
}

However if would be nice if you could specify a complete ontology like the Gene Ontology or Snomed Ontology. Like

<Gene>
{
  ex:function      type::GO:Molecular_Function. 
}

The function property can point to any of the subclasses of the Molecular_Function class in the GO ontology.

Classes/terms/enumeration values within this 'extended' enumeration can define concepts that are subconcepts of other classes/terms/enumeration values.

Discussion 4, Support for named graphs

Proposed for 1.1 See the ShEx/Graph_Named_Graphs page

Use Cases

Enable validation outside of a single named graph:

Dataset:

 Default graph: { <s> :lookInGraph <G1> }
 <G1>: { <s> :p2 :o2 }

Schema:

 <S> { :lookInGraph GRAPH{ @<GShape> } }
 <GShape> { :p2 . }

Discussion 5, Unique