ISO/IEC 23001-2:2008 - Fragment Request Units (FRU)
Overview
ISO/IEC 23001-2:2008 defines the Fragment Request Unit (FRU) technology for MPEG systems. The standard specifies a syntax and semantics for expressing requests for fragments of XML, and how those requests are used in XML‑based systems (for example ISO/IEC 15938-1 and ISO/IEC 23001-1). FRUs enable selective retrieval and node‑by‑node navigation of remote XML documents so that only the XML fragments of interest are transmitted-important for resource‑constrained environments such as mobile devices and set‑top boxes.
Key topics and requirements
- FRU syntax and semantics: Standardized element structure and attributes that represent navigation and query operations against an XML source document.
- Request and response model: Definitions of FRU Request and FRU Response containers, and the roles of FRU processor, FRU response processor, and context processor.
- Navigation and Query modes: Support for node‑by‑node and level‑by‑level navigation and for querying (e.g., using XPath expressions) to select fragments.
- Fragment semantics: Definition of what constitutes an XML fragment (may not be a complete well‑formed document but conforms to XML content production).
- Interoperability rules: How FRUs integrate with systems layers and delivery layers (transport agnostic - examples include SOAP/HTTP and optional binary encoding with BiM).
- Response content: Use of Fragment Update Units (FUUs) to deliver returned XML fragments and namespace handling details (e.g., default namespace attributes).
- Normative references and schemas: Ties to W3C XML, XML Namespaces, XML Schema, XPath, RFC 3986 (URI), and includes annexes such as a W3C XML Schema for FRUs and guidance for use in ISO/IEC 15938-1.
Applications and who uses it
- Developers and architects of MPEG systems, multimedia metadata (MPEG‑7 / ISO/IEC 15938), and MPEG‑B (Binary MPEG format for XML).
- Implementers of XML delivery systems for constrained devices (mobile apps, set‑top boxes, embedded systems) who need to minimize bandwidth, storage, and processing by fetching partial XML.
- Systems integrating remote XML navigation or XPath queries, where selective retrieval, incremental loading, or node navigation is required.
- Vendors building middleware, content delivery platforms, and standards‑compliant tools that support BiM encoding and FRU transport.
Related standards
- ISO/IEC 23001-1 (BiM - Binary MPEG format for XML)
- ISO/IEC 15938-1 (MPEG‑7 Systems)
- W3C XML, XML Namespaces, XML Schema, XPath
- IETF RFC 3986 (URI syntax)
Keywords: ISO/IEC 23001-2:2008, Fragment Request Unit, FRU, XML fragments, MPEG systems, BiM, ISO/IEC 15938-1, XPath, resource‑constrained devices, navigation, query.
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