Codespace - nick-knowles/NeTEx GitHub Wiki

A CODESPACE defines the context within which an identifier of an object in a document is unique (ie a namespace for data).

The data exchanged with NeTEx may come from multiple sources and many diffiernet stakeholders, is exchanged repeatedly, and may be integrated with other data sets in many different ways. It is therefore essential to make sure that identifiers are unique and stable throughout an object’s lifecycle. In NeTEx, the actual structure of an identifier can be arbitrary and is indicated by its CODESPACE, which also establishes a context within which a given code structure is unique. Multiple CODESPACEs can be used within a document.

Examples of using codespaces

Each CODESPACE has an identifier which may be used in the document . For example, The following are some fictional examples of Codespace PREFIXES use for different identifiers:

  <TopographicPlace id=”nptgLocality:E00034531”>,  where  ‘nptgLocality = http://naptan.org.uk/nptgLocality  

  <ScheduledStopPoint id=”smirt:454e74”> , where ‘smirt’ = http://www.hdfmobilites.fr/smirt/stops	 

  <Line id=”llp:22”> , where ‘llp’ = http://llp.sl/lines	 

  <Route id=”enturRoute:985a”> , where	‘entRoute’ = http://www.entur.org/routes	 

  <ServiceJourney id=”db:107678”>, where| ‘db’ = http://bahn.de/reise	 

  <StopPlace id=”ratpStop:43289”>, where ‘raptStop’ = http://ratp.fr	 

  <StopPlace id=”naptStop:199G98765431”>, where‘naptStop’ = http://naptan.org.uk/stops

A CODESPACE is specified as a path expression by using internet domains which have a mechanism for registering global uniqueness, for example tfl.gov.uk, foo.com, or xxx.de. These can be declared on an frame

Example

The following example shows the declaration of two codespaces in a VERSION FRAME, one of which is set as the default for the frame. Note that the codespace prefix used in front of data elemenst can be different from the codespace identifier. ``` <Codespace id="frst_data frst https://www.firstgroup.com/york First data fxc http://netex.org.uk/fxc FXC metadata epd</ CodespaceRef>

	</codespaces>
	<FrameDefaults>
		<DefaultCodespaceRef ref="frst_data"/>
		<DefaultResponsibilitySetRef version=”any” ref="frst:data"/>
	</FrameDefaults

```

Further points

The use of CODESPACEs in NeTEx allows an economical encoding of identifiers in an XML document so that a common prefix does not have to repeated on each element in the document.

If the CODESPACE is the default CODESPACE for the frame, it may be omitted from elements in the frame.

A CODESPACE may also imply additional rules for the internal format of the code, such as minimum and maximum lengths, permitted characters, or a specific substructure, but any such rules are external to NeTEx and must be agreed by the implementers of producers and consumers of a dataset. The purpose of a CODESPACE is to make NeTEx neutral as to the identifier systems used and so allow the concurrent existence of many different code systems within the same document. CODESPACEs avoid any unnecessary requirement for a common identifier structure and furthermore allow for extremely compact references with a document.

An application processing a document is expected to understand any rules peculiar to interpreting a specific CODESPACE .

Using CODESPACEs to manage the distributed allocation of codes

One or more CODESPACE ASSIGNMENTs can also be associated with each ADMINISTRATIVE ZONE to reserve the use of a specific prefix or range of code values for the allocation of identifiers to new entities within that zone. This allows the allocation of codes for new entities to be distributed to spearate ORGANISATIONSresponsible for each ADMINISTATIVE AREA, i.e. the central 'registar' can delegate the responsibility to issue unique codes to other organisations.

Combining different types of element into the same CODESPACE

A single CODESPACE may cover multiple types of different element, provided the identifiers and class context are unique within it (see discussion of Xml Integrity rules and NeTEx Identifier uniqueness.

For example, TOPOGRAPHIC PLACEs in the UK National Public Transport Gazetteer all begin with ‘E,’ UK NaPTAN SCHEDULED STOP POINT ids all begin with a numeric area prefix and have a 0, or 1 in the fourth place, while UK NaPTAN STOP AREA ids are similar to SCHEDULED STOP POINTs but have a ‘G’ in the fourth place. Thus they have distinct scopes and – so could all be placed in a single ‘NaPTAN’ CODESPACE.