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Martynas Jusevičius edited this page Jan 14, 2026 · 3 revisions

Package Structure

Each package consists of:

packages/<package-name>/
├── ns.ttl         # Ontology with template blocks (ldh:template)
└── layout.xsl     # XSLT stylesheet with custom templates

Package metadata is Linked Data that resolves from the package URI (e.g., https://packages.linkeddatahub.com/skos/#this).

Example: SKOS Package

packages/skos/
├── ns.ttl         # SKOS vocabulary with ldh:template blocks
└── layout.xsl     # XSLT templates for SKOS concepts, schemes, collections

Metadata for this package resolves from https://packages.linkeddatahub.com/skos/#this.

How Packages Work

1. Package Metadata

Package metadata resolves as Linked Data from the package URI using standard LinkedDataHub properties:

@prefix lapp: <https://w3id.org/atomgraph/linkeddatahub/apps#> .
@prefix ldt:  <https://www.w3.org/ns/ldt#> .
@prefix ac:   <https://w3id.org/atomgraph/client#> .

<https://packages.linkeddatahub.com/skos/#this> a lapp:Package ;
    rdfs:label "SKOS Package" ;
    dct:description "SKOS vocabulary support with custom templates" ;
    ldt:ontology <https://raw.githubusercontent.com/AtomGraph/LinkedDataHub-Apps/master/packages/skos/ns.ttl#> ;
    ac:stylesheet <https://raw.githubusercontent.com/AtomGraph/LinkedDataHub-Apps/master/packages/skos/layout.xsl> .

Note: Uses standard ldt:ontology and ac:stylesheet properties instead of inventing new ones.

2. Ontology (ns.ttl)

Contains two layers:

A. Vocabulary Import

Imports the external vocabulary using owl:imports:

<https://raw.githubusercontent.com/AtomGraph/LinkedDataHub-Apps/master/packages/skos/ns.ttl#> a owl:Ontology ;
    owl:imports <http://www.w3.org/2004/02/skos/core> .

B. Template Blocks (ldh:template)

SPARQL-based views attached to RDF types from the imported vocabulary:

skos:Concept ldh:template ns:NarrowerConcepts .

ns:NarrowerConcepts a ldh:View ;
    dct:title "Narrower concepts" ;
    spin:query ns:SelectNarrowerConcepts .

ns:SelectNarrowerConcepts a sp:Select ;
    sp:text """
    SELECT DISTINCT ?narrower
    WHERE { GRAPH ?graph { $about skos:narrower ?narrower } }
    ORDER BY ?narrower
    """ .

3. XSLT Stylesheet (layout.xsl)

XSLT templates using system modes to override default rendering:

<!-- Hide properties from default property list -->
<xsl:template match="skos:narrower | skos:broader" mode="bs2:PropertyList"/>

<!-- Override XHTML head elements -->
<xsl:template match="*" mode="xhtml:Style">
    <!-- Custom styles -->
</xsl:template>

Available system modes include bs2:* (Bootstrap 2.3.2 components), xhtml:* (XHTML elements), and others.

Installing Packages

Method 1: CLI Script

install-package.sh \
  -b https://localhost:4443/ \
  -f ssl/owner/cert.pem \
  -p Password \
  --package https://packages.linkeddatahub.com/skos/#this

Method 2: From Application Install Script

# In LinkedDataHub-Apps/demo/skos/install.sh
install-package.sh \
  -b "$base" \
  -f "$cert_pem_file" \
  -p "$cert_password" \
  --package "https://packages.linkeddatahub.com/skos/#this"

Prerequisites

Before installing packages, master stylesheets must exist in the webapp directory:

  • /static/xsl/layout.xsl - End-user application master stylesheet
  • /static/xsl/admin/layout.xsl - Admin application master stylesheet

Default templates are provided at:

src/main/webapp/static/xsl/layout.xsl
src/main/webapp/static/xsl/admin/layout.xsl

These files should be deployed with the application. End-user stylesheet contains:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    exclude-result-prefixes="xs">

    <!-- System stylesheet (lowest priority) -->
    <xsl:import href="../com/atomgraph/linkeddatahub/xsl/bootstrap/2.3.2/layout.xsl"/>

    <!-- Package stylesheets will be added here by InstallPackage endpoint -->

</xsl:stylesheet>

What Installation Does

When you install a package, the system:

  1. Fetches package metadata from the package URI
  2. Hashes the package ontology URI using SHA-1 to create a unique document slug
  3. Downloads package ontology (ns.ttl) and PUTs it as a document to ${admin_base}ontologies/{hash}/ where {hash} is the SHA-1 hash of the ontology URI
  4. Adds owl:imports from the namespace ontology to the package ontology in the namespace graph (${admin_base}ontologies/namespace/)
  5. Clears and reloads the namespace ontology from cache to pick up the new imports
  6. Downloads package stylesheet (layout.xsl) and saves it to /static/{package-path}/layout.xsl where {package-path} is derived from the package URI (e.g., com/linkeddatahub/packages/skos/ for https://packages.linkeddatahub.com/skos/)
  7. Updates master stylesheet at /static/xsl/layout.xsl by adding import: 
    <xsl:import href="../com/atomgraph/linkeddatahub/xsl/bootstrap/2.3.2/layout.xsl"/>  <!-- System -->
<xsl:import href="../com/linkeddatahub/packages/skos/layout.xsl"/>  <!-- Package (added) -->
  8. Adds import to application (TODO - currently manual): <app> ldh:import <package-uri>

Note: The master stylesheet must already exist or installation will fail with InternalServerErrorException.

Architecture

Installation-Time vs Runtime

Packages use installation-time composition, NOT runtime composition:

  • ✅ Package content is integrated during installation (via JAX-RS endpoints)
  • ✅ Ontology and XSLT are pre-composed before being loaded
  • ✅ No runtime overhead
  • ❌ No dynamic package loading at request time

JAX-RS Endpoints

On the admin application

  • POST /packages/install - Installs a package

    • Parameter: package-uri (form-urlencoded)
    • Requires owner/admin authentication
    • Delegates authenticated agent credentials for PUT requests

  • POST /packages/uninstall - Uninstalls a package

    • Parameter: package-uri (form-urlencoded)
    • Requires owner/admin authentication

File System Structure

After installing the SKOS package:

webapp/
├── static/
│   ├── com/
│   │   └── linkeddatahub/
│   │       └── packages/
│   │           └── skos/
│   │               └── layout.xsl          # Package stylesheet
│   └── xsl/
│       ├── layout.xsl                      # End-user master stylesheet
│       └── admin/
│           └── layout.xsl                  # Admin master stylesheet

SPARQL Data Structure

# In admin SPARQL endpoint at <${admin_base}ontologies/{hash}/>
# Package ontology stored as a document where {hash} is SHA-1 of ontology URI
<https://raw.githubusercontent.com/AtomGraph/LinkedDataHub-Apps/master/packages/skos/ns.ttl#> a owl:Ontology ;
    # ... package ontology content ...

# In admin SPARQL endpoint (namespace graph at <${admin_base}ontologies/namespace/>)
# Namespace ontology imports package ontology
<https://localhost:4443/ns#> a owl:Ontology ;
    owl:imports <https://raw.githubusercontent.com/AtomGraph/LinkedDataHub-Apps/master/packages/skos/ns.ttl#> .

# In system.trig (application config)
<urn:linkeddatahub:apps/end-user> a lapp:EndUserApplication ;
    ldt:ontology <https://localhost:4443/ns#> ;
    ac:stylesheet <static/xsl/layout.xsl> ;  # Master stylesheet

Available Packages

List of available packagcan be found in the LinkedDataHub-Apps repository.

Creating New Packages

  1. Create directory: packages/<name>/
  2. Write ns.ttl with vocabulary and template blocks
  3. Write layout.xsl with XSLT templates (using system modes like bs2:*, xhtml:*, etc.)
  4. Publish package metadata as Linked Data at https://packages.linkeddatahub.com/<name>/#this
  5. Ensure the metadata contains ldt:ontology and ac:stylesheet properties pointing to the package resources

Vocabulary Reference

LAPP Vocabulary (https://w3id.org/atomgraph/linkeddatahub/apps#)

  • lapp:Package - Package class

Standard Properties (Reused)

  • ldt:ontology - Points to package ontology URI (from LDT vocabulary)
  • ac:stylesheet - Points to package stylesheet URI (from AtomGraph Client vocabulary)

Notes

  • Packages are declarative only (RDF + XSLT, no Java code)
  • Package ontologies use owl:imports (handled automatically by Jena)
  • Package stylesheets use xsl:import (handled by master stylesheet generation)
  • Template blocks (ldh:template) are separate from XSLT overrides
  • Both mechanisms work independently and complement each other

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