What is an information unit in iiRDS?

It is the abstract base class for every piece of content that carries iiRDS metadata. In practice each unit is typed as a Document, Topic, Fragment or Package.

Can I type content directly as iirds:InformationUnit?

No. The specification states that iiRDS generators must not use the class directly and must use one of its subclasses.

Does an information unit have to be a file?

No. A unit may refer to a whole file, to part of a file through a selector, or to no file at all, such as a document that exists only as a structure of topics.

Can an information unit be a blank node?

No. Every instance of an InformationUnit subclass must have an IRI, so it can be referenced from other data.

What is the difference between an information unit and a rendition?

The information unit carries the meaning and the metadata. A rendition is only a file of that unit, such as HTML or PDF, linked with iirds:has-rendition.

Do topics inherit metadata from the document they appear in?

Not automatically. The specification does not define metadata inheritance between information units, so each unit should carry the metadata it needs.

Wiki · iiRDS core concepts · Information units

iiRDS InformationUnit: the abstract base class for metadata-bearing content

Every piece of content in an iiRDS package that carries metadata is an information unit. The class iirds:InformationUnit is abstract: generators never use it directly, but always one of its four subclasses, Document, Topic, Fragment or Package. Understanding this class explains the core design decision of iiRDS: metadata such as product, lifecycle phase or qualification is attached to a unit of meaning, not to a file. Files are renditions of a unit, and language versions are grouped by an information object. This guide explains what an information unit is, how the four subclasses differ in granularity, how the unit relates to renditions and information objects, what the specification requires (an IRI, no blank nodes), and how the concept maps to topic-based authoring, legacy PDF migration, MedTech documentation and AI retrieval.

Valid for iiRDS 1.3Last reviewed September 25, 2026Level: Introductory

Technical documentation
Machinery
MedTech
AI retrieval

Definition

In iiRDS (intelligent information Request and Delivery Standard), InformationUnit is the abstract base class for every piece of intelligent information that carries metadata. It is never used on its own: each information unit is a Document, a Topic, a Fragment or a Package.
Based on iiRDS Specification 1.3, iiRDS Consortium

The specification defines an information unit as a piece of digitally encoded information and describes it as the link between user assistance content and its metadata. The class itself is abstract. An iiRDS generator must type each unit as a Document, a Topic, a Fragment or a Package, and every instance must have an IRI instead of being a blank node.

Document, Topic and Fragment describe the same kind of thing at different granularities, from a complete manual down to a single warning. Package is special: it represents the delivery package itself, and each iiRDS package has exactly one Package instance.

An information unit is not a file. A unit may point to a whole file, to part of a file through a selector, or to no file at all, for example a document assembled only from topics. Its files are renditions, and its language versions and revisions can be grouped under one information object.

In one sentence

An iiRDS information unit is the addressable piece of content, identified by an IRI, to which all descriptive metadata is attached, always typed as one of four concrete subclasses.

Example

A manufacturer of packaging machines delivers the documentation for one model as an iiRDS package. The operating manual is a Document with a PDF rendition. The service content is authored as topics, such as “Replacing the air filter”, each with an HTML rendition. The warning “Disconnect the mains supply before opening the housing” is a Fragment, and the package itself is described by one Package instance. All four are information units: each has its own IRI and carries metadata for the machine model, the lifecycle phase and the component it concerns. A service portal can therefore answer “show me all maintenance content for the air filter” across all four granularities.

How it applies

Technical documentation

The information unit is where metadata lives in iiRDS. Product variants, lifecycle phases, information subjects and qualifications are related to the unit, not to its files. One topic with two renditions therefore needs its metadata only once, and a delivery portal can filter by product or phase without copying content.

Migration

Legacy content does not have to be rewritten first. An existing PDF manual can enter a package as a Document with one rendition, and chapters can later become separate units through selectors. The unit model lets granularity grow step by step, from whole documents to topics and fragments.

MedTech

Instructions for use and their language versions can each be modeled as a unit with its own revision, language and content lifecycle status. Grouping them under one information object shows which versions carry the same content. The model supports traceable delivery; it does not by itself make a deliverable compliant.

AI and retrieval

Information units are pre-labeled chunks with stable IRIs. A retrieval pipeline can index the text of a rendition while taking product, phase and topic type from the unit’s metadata, and it can cite the IRI as the source. That context would otherwise have to be inferred from the text.

InformationUnit vs. InformationObject vs. Rendition

Concept	What it is	Carries metadata	Has files
InformationUnit	Concrete content in one language and revision	Yes	Through renditions
InformationObject	The shared identity of versions and translations	Only identities (`iirds:has-identity`)	No
Rendition	One file of a unit, with path and MIME type	No	Is the file

Each unit links to at most one information object with iirds:is-version-of and to its files with iirds:has-rendition.

In RDF

The four subclasses in use, each with an IRI; nothing is typed as iirds:InformationUnit itself. Shown in Turtle for readability — inside a package, metadata.rdf is written in RDF/XML.

@prefix iirds: <http://iirds.tekom.de/iirds#> .

<https://example.com/iirds/packages/machine-x200> a iirds:Package ;
    iirds:iiRDSVersion "1.3" .

<https://example.com/iirds/operating-manual> a iirds:Document ;
    iirds:has-document-type iirds:OperatingInstructions ;
    iirds:is-part-of-package <https://example.com/iirds/packages/machine-x200> .

<https://example.com/iirds/replace-air-filter> a iirds:Topic ;
    iirds:relates-to-product-lifecycle-phase iirds:Maintenance ;
    iirds:is-part-of-package <https://example.com/iirds/packages/machine-x200> .

<https://example.com/iirds/warning-mains-supply> a iirds:Fragment ;
    iirds:is-part-of-package <https://example.com/iirds/packages/machine-x200> .

In topic-based authoring and modular architectures

In topic-based authoring, the modules of a component content management system or the topics of a DITA project become information units when they are published with iiRDS metadata. The authoring unit and the delivery unit do not have to match one to one: a map can be delivered as a Document, its topics as Topics, and reusable warnings as Fragments. In modular delivery architectures, the unit is the contract between systems. The authoring side guarantees an IRI and metadata per unit; the consuming portal or assistant decides how to assemble, filter and display the units. Navigation between units is modeled separately with directory nodes, so the same unit can appear in several structures.

Concept cluster

How this concept connects to the other iiRDS core concepts.

Also searched as

iiRDS InformationUnit
iirds:InformationUnit
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InformationUnit

Questions this article answers:

what is an information unit in iiRDS
iiRDS InformationUnit subclasses Document Topic Fragment Package
can I use iirds:InformationUnit directly
difference between information unit and rendition in iiRDS

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Frequently asked questions

What is an information unit in iiRDS?: It is the abstract base class for every piece of content that carries iiRDS metadata. In practice each unit is typed as a Document, Topic, Fragment or Package.
Can I type content directly as iirds:InformationUnit?: No. The specification states that iiRDS generators must not use the class directly and must use one of its subclasses.
Does an information unit have to be a file?: No. A unit may refer to a whole file, to part of a file through a selector, or to no file at all, such as a document that exists only as a structure of topics.
Can an information unit be a blank node?: No. Every instance of an InformationUnit subclass must have an IRI, so it can be referenced from other data.
What is the difference between an information unit and a rendition?: The information unit carries the meaning and the metadata. A rendition is only a file of that unit, such as HTML or PDF, linked with iirds:has-rendition.
Do topics inherit metadata from the document they appear in?: Not automatically. The specification does not define metadata inheritance between information units, so each unit should carry the metadata it needs.

Conclusion

The information unit is the anchor of the iiRDS metadata model. Choosing the right subclass decides the granularity of delivery, and attaching metadata to the unit rather than to its files lets one piece of content serve print, portals and retrieval systems without duplication.