Dev:Semantic Constraints
Semantic constraints
XML Schema Definitions (XSDs) offer a variety of possibilities to define syntactic constraints, describing the syntax of an XML file, including the type and multiplicity of an element. For example in railML® 2, it is possible to describe and validate that a <train> must reference one or more <trainPart>s, that all <trackElements> must have a position on the <track>, that the length of a <tunnel> is a decimal number and that allowed positions of <couplers> are at the front, rear or both ends of a <wagon>. However, XML Schema Definitions are not able to express a constraint on one element or attribute that depends on the value or existence of another element or attribute. One example is that an XSD cannot express that a departure time must be greater than or equal to the arrival time, or that it does not make sense to specify a stopOnRequest and at the same time that the train is not allowed to stop. Such rules restricting the contents, or semantics, of one element or attribute depending on other content, are called semantic constraints.
Semantic constraints are as important as syntactic constraints. If they are ignored, other software may not be able to handle your railML® files, or may interpret the contents in different ways. Therefore, their implementation will be checked during certification.
Elements with approved semantic constraints are listed in Category:Semantic constraints. On the element documentation pages, the semantic constraints can be found in a dedicated chapter below the syntactic constraints. Proposed semantic constraints are listed in Category:Semantic constraints_proposed. A list of the semantic constraints by introduction date of a can be found below.
Every application of railML® has to be checked not only on XSD compliance but also on the obedience to the semantic constraints.
How to introduce Semantic Constraints
Constraints that can be described by XML Schema Definitions (XSDs) should be implemented syntactically in the schemas. Please, follow the guideline for participating in the development process. If a constraint cannot be described by XML Schema Definitions, you can propose a semantic constraints.
Semantic constraints can be proposed either by one of the railML® working groups (link to the railML® website) or suggested by anyone through a post in the forum (link to the railML® website).
If there is consensus in a working group to add a new semantic constraint, a post will be made in the forum and the proposed constraint will be added to the element documentation using Template:Semcon, with status=proposed
and added to the list below. If there are no objections in the forum, it will be approved after six weeks and implemented in the wiki with status=approved
.
If you see the need for a semantic constraint beyond the schema, please discuss it in the forum (link to the railML® website) and then add a proposal in the element documentation using Template:Semcon, with status=proposed
. Please also add the proposal to the list below! If a consensus is reached in the forum, the proposal will be accepted, it will implemented in the wiki with status=approved
.
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Design guidelines
- Implement a seperate semantic constraint for every rule.
- Use the template with all mandatory arguments according to Template:SemanticConstraint.
- Record the semantic constraint on the respective list below (Dev:Semantic_Constraints/table2 for railML® 2 and Dev:Semantic_Constraints/table3 for railML® 3).
- assign a serial id to the semantic constraint according to the appropriate list below.
Current Constraints as of railML 3.2
View/edit list on the separate source page.
Element | ID | Proposal date | Date of acception | Date of deprecation | Description |
---|---|---|---|---|---|
<TT:operationalTrainSectionPart> | TT:001 | 2022-09-15 | 2022-10-13 | There is always only a single successor and predecessor for an <operationalTrainSectionPart> in the chain of <operationalTrainSectionPart>s that are linked via the attribute @next. | |
<TT:operationalTrainVariant> | TT:002 | 2023-01-12 | 2023-04-06 | When calculating which <operationalTrainVariant> of an <operationalTrain> is valid on a particular day always a maximum of one active <operationalTrainVariant> shall be the result. If the result is more than one <operationalTrainVariant>, all except one shall be marked as <isCancelled> or <isOnRequest>. | |
<TT:commercialTrainVariant> | TT:003 | 2023-01-12 | 2023-04-06 | When calculating which <commercialTrainVariant> of an <commercialTrain> is valid on a particular day always a maximum of one active <commercialTrainVariant> shall be the result. If the result is more than one <commercialTrainVariant>, all except one shall be marked as <isCancelled> or <isOnRequest>. | |
<TT:operationalTrainSection> | TT:004 | 2022-01-12 | 2023-03-09 | The itinerary sections of an <operationalTrainVariant>, defined by the <operationalTrainSection>s and their respective <range>s, that are not <isCancelled> and not marked as <isOnRequest>, must be pairwise disjoint, except for their respective first and last <baseItineraryPoint>s. | |
<TT:operationalTrainSection> | TT:005 | 2022-01-12 | 2023-03-09 | The first(last) <baseItineraryPoint> of each <operationalTrainSection> within an <operationalTrainVariant> must either be the referenced <itinerary>'s first(last) <baseItineraryPoint>, or coincide with another section's last(first) <baseItineraryPoint>. | |
<TT:commercialTrainSection> | TT:006 | 2022-01-12 | 2023-03-09 | The itinerary sections of an <commercialTrainVariant>, defined by the <commercialTrainSection>s and their respective <range>s, that are not <isCancelled> and not marked as <isOnRequest>, must be pairwise disjoint, except for their respective first and last <baseItineraryPoint>s. | |
<TT:commercialTrainSection> | TT:007 | 2022-01-12 | 2023-03-09 | The first(last) <baseItineraryPoint> of each <commercialTrainSection> within an <commercialTrainVariant> must either be the referenced <itinerary>'s first(last) <baseItineraryPoint>, or coincide with another section's last(first) <baseItineraryPoint>. | |
<RTM:isValid>, <CO:validityTime:period> | IS:001 | 2024-01-15 | 2024-02-26 ETCS WG
2024-03-22 SCTP WG 2024-04-15 NEST WG |
Starting time stamp (e.g. "from") shall be lower or equal any ending time stamp (e.g. "to") if both are given. Must not overlap with other validity periods. | |
<IS:trainProtectionElement> | IS:002 | 2021-02-26 | 2024-02-26 ETCS WG
2024-03-22 SCTP WG 2024-04-15 NEST WG |
<trainProtectionElement> shall only be used for national and/or legacy train protection systems. ETCS-based systems must not be modeled using <trainProtectionElement>. | |
<IS:levelCrossingIS> | IS:003 | 2023-10-23 | 2024-02-26 ETCS WG
2024-03-22 SCTP WG 2024-04-15 NEST WG |
<levelCrossingIS> should not have a <crossesElement> child of type railway. This case should be represented either by a <crossing> in case of a simple crossing, or by a <switchIS> of type doubleSwitchCrossing or singleSwitchCrossing. | |
<IS:underCrossing>, <IS:overCrossing> | IS:004 | 2023-10-23 | was declined | 2024-02-26 | should only have a <crossesElement> child of type railway when railway crosses railway (not on the same level!). |
<IS:signalConstruction> | IS:005 | 2024-01-22 | 2024-03-22 SCTP WG
2024-04-15 NEST WG |
@height and @positionAtTrack should not be used with @type=virtual. | |
<IS:line> | IS:006 | 2024-01-29 | 2024-02-26 ETCS WG
2024-04-15 NEST WG |
each line with own mileage should always be associated with its own <linearPositioningSystem>, i.e. Advanced example of railML has three lines with their own mileages, thus should have thee <linearPositioningSystem>s. 2024-03-22 SCTP WG - GUI implementation not clear | |
<IS:border> | IS:007 | 2024-01-29 | 2024-08-09 SCTP WG |
if @isOpenEnd="true" then @type should be set as @type="area". | |
<IS:netElement> | IS:008 | 2024-02-02 | 2024-08-09 SCTP WG |
Aggregation of net elements should follow the tree data structure. See figure below. This means that no two (mesoscopic) net elements can aggregate same (microscopic) net element. In other words, (microscopic) net element can be aggregated by at most one (mesoscopic) net element. | |
<IS:netElement> | IS:009 | 2024-02-02 | 2024-08-09 SCTP WG |
Linear (geometric) coordinates (explicit or implicit, e.g. calculated as a sum of the coordinate of beginning and the length of the net element) of the same place represented at different levels of aggregation should have the same value. In the figure below (linear) coordinate the coordinate of e.g. end of ne1 should be same as one of ne1.2. | |
<IS:netElement> | IS:010 | 2024-02-26 |
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<IS:netElement> | IS:011 | 2024-02-29 | 2024-08-09 SCTP WG |
Aggregation must not happen within the same level of detail. In the figure below, element 1.1 must not aggregate element 1.2. This means that aggregating and aggregated net elements must not be referred from the same <level> | |
<RTM:spotLocation> | IS:012 | 2024-03-04 | 2024-04-19 SCTP WG
2024-05-13 ETCS WG |
@pos should have only positive values because it's a distance, thus -1 is not a valid value | |
functional infrastructure and geometry entities | IS:013 | 2024-03-25 |
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<RTM:linearPositioningSystem> | IS:014 | 2024-04-08 | 2024-04-15 NEST WG
2024-04-19 SCTP WG |
@startMeasure and @endMeasure are start and end values of a railway <IS:line> associated with <RTM:linearPositioningSystem> not max and min values of a current file with e.g. line section.
| |
<IS:netRelation> | IS:015 | 2024-04-22 | 2024-08-09 SCTP WG | There must be no "inverse" net relations in the topology, i.e. if "nr1 elemeneA ne1", "nr1 elementB ne2" and "nr2 elemeneA ne2", "nr2 elementB ne1" then topology is not valid. See invalid code below. | |
<IS:gradientCurve> | IS:016 | 2024-05-31 | @gradient should not be used if @curveType="mixed". Instead of @gradient, @deltaGradient should be used. | ||
<IS:trainProtectionElement> | IS:017 | 2009-10-17 | 2009-10-17 |
Users can refer to the train protection system using the attribute @trainProtectionSystem that shall link to the codelist (link to the railML® website) TrainProtectionSystems.xml (link to the railML® website), section trainProtectionSystemsAtTrack. Only if this list does not contain the specific train protection system to be modelled, it shall be described in its functionality using attributes @medium and @monitoring. | |
<IS:opEquipment> | IS:018 | 2024-08-26 |
Any functional infrastructure element that belongs to an <operationalPoint> may be listed as its equipment. This may be done by adding it to a specific container, such as <ownsPlatform>, <ownsTrack> and <ownsSignal> or it may be added to the generic container <ownsInfrastructureElement>. Any such added infrastructure element must be added to the most specific container available. No element shall be part of two such containers. If no specific container for the functional infrastructure element exists, it shall be listed in the generic container. Example: a <signalIS> must not be added to <ownsInfrastructureElement>. It shall be added to <ownsSignal>. As there is no container for levelCrossings a <levelCrossingIS> belonging to an <operationalPoint> shall be added to <ownsInfrastructureElement>. | ||
<IS:infrastructureState> | IS:019 | 2024-09-03 | 2024-09-13 SCTP WG |
When calculating which <infrastructureState> of an <infrastructure> is valid on a particular time always a maximum of one active <infrastructureState> shall be the result. See examples below. |