Dev:SemanticConstraints

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🗒️ This page is mirrored from page Dev:SemanticConstraints in The railML® 3 Wiki.

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

Before proposing a semantic constraint, please note:

  • The purpose of semantic constraints is to restrict the allowed values of one property depending on the values of other properties.
  • Descriptions of the meaning of an element or property belong in the schema documentation. This includes how (not) to interpret or use possible values of a property.
  • 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 constraint.

Semantic constraints can be proposed either by one of the railML® working groups (link to the railML® website) or suggested by anyone through the following process:

  1. If you see the need for a semantic constraint beyond the schema, please propose it in the forum (link to the railML® website). The responsible schema coordinator will bring it to the relevant working group or directly to the group of coordinators.
  2. 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. The other working groups will also be notified, so they can check if the proposed constraint affects their use cases.
  3. After the community has been given a reasonable time to raise any objections in the forum, the coordinators will decide if the proposed semantic constraint is approved. Following this decision, the documentation will be updated accordingly.
🗒️ Semantic constraints that have been proposed before the 10th of December 2018 shall be considered as approved until decided otherwise.
🗒️ The process above was revised in January 2025, adding a decision by the group of coordinators to replace automatic approval when no objections were raised within six weeks after a new semantic constraint was proposed in the forum. The coordinators will also review the semantic constraints listed below, as not all of them have followed the previous process. The list may therefore change.


Design guidelines

Current Constraints as of railML 2.5

View/edit list on the separate source page.

Element ID Proposal date Date of acceptance Date of deprecation Description
<TT:timetablePeriod> TT:001 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with other validity periods.
<TT:specialService> CO:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given.
<TT:operatingPeriodRef> CO:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given.
<TT:operatingPeriod> CO:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given.
<TT:operatingDay> TT:019 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with other <operatingDay> validity periods of the same enclosing <operatingPeriod>.
<TT:circulation> CO:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given.
<TT:blockPart> CO:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given.
<RS:designator> (introduced with version 2.5) RS:001 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with the validity periods of other entries of the same register of the same enclosing <state>.
<RS:operator> RS:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with other <operator> validity periods of the same enclosing <vehicle>/<classification>.
<RS:owner> (introduced with version 2.5) RS:003 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with other <owner> validity periods of the same enclosing <vehicle>/<classification>.
<RS:state> RS:004 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with other <state> validity periods of the same enclosing <vehicle>/<states>.
<IS:state> IS:020 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with other <state> validity periods of the same enclosing <states> collection. See also Dev:Defining temporal availability of infrastructure elements and speed profiles.
<IS:state (with length)> IS:021 2018-11-12 2019-03-21 Must not overlap with other <state (with length)> validity periods of the same enclosing <states (with length)> collection. See also Dev:Defining temporal availability of infrastructure elements and speed profiles.
<IS:designator> CO:001 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with the validity periods of other entries of the same register of the same enclosing element.
<CO:designator> (introduced with version 2.5) CO:001 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given. Must not overlap with the validity periods of other entries of the same register of the same enclosing element.
<CO:phase> (introduced with version 2.5) CO:002 2018-11-12 2019-03-21 Any starting time stamp (as it may result e.g. from a combination of startDate and startTime) shall be lower or equal any ending time stamp (e.g. endDate) if both are given.
<TT:ocpTT> TT:002 2018-10-25 2019-06-20 The attribute sequence is shall be increasing according to the train path.
<TT:ocpTT> 2018-10-25 discarded No ocpRef is allowed to occur more than one time in the same <trainPart>
<TT:blockPart> TT:003 2019-07-13 2019-07-18 By means of a <blockPart> it is possible to model both journeys with and without reference to a <trainPart> within a roster, as well as services without change of location (without reference to a <trainPart>). These 3 basic types are distinguished by the attribute mission. The following table presents the semantic constraints: see table
<TT:blockPart> TT:004 2019-07-20 2019-07-18 vehicleRef and formationRef shall not be used within the same blockPart, since a blockPart is either one for a certain vehicle or one for a whole formation. The only exception to this rule is if the formation consists of only one vehicle that is also specified via vehicleRef
<TT:rostering> TT:005 2019-05-22 2019-06-25 vehicleRef and formationRef are to be used exceptional since the circulation plan is either one for a certain vehicle or one for a whole formation. The only exception to this rule is if the formation consists of only one vehicle that is also specified via vehicleRef
<TT:stopDescription> TT:006 2018-09-03 2019-06-20 Constraints between the attributes <ocpTT>.ocpType, <stopDescription>.guaranteedPass, .commercial, .onOff, .stopOnRequest and .operationalStopOrdered
<TT:stopDescription> (Stop on request / More than one stop type per OCP) TT:007 2019-06-19 discarded 2020-04-23
<TT:trackInfo> TT:009 2018-08-21 2019-06-20 The operating days of the <operatingPeriodRef>s of the individual <trackInfo> entries must be disjoint and must not contain more traffic days than the parent <trainPart>. If fewer traffic days are provided in the <trackInfo> entries than the parent <trainPart> contains, the information (e.g. attribute trackInfo) of the parent <ocpTT> must be evaluated for these operating days.
<TT:times> TT:011 2019-06-19 discarded
<TT:times> TT:012 2019-06-19 2022-06-02 When @scope='actual' is used, then the operating period and/or timetable period specified at the trainpart level shall refer to only one operating day. Like this the operating day to which the actual times refer is defined.
<TT:times> TT:013 2019-06-19 discarded
<TT:times> (Arrival times for passing OCP's) TT:014 2019-06-19 2022-06-02 @arrival is not to be specified if the attribute ocpType of the parent <ocpTT> has the value pass - use departure for run-through (passing) times; This is in line with the definition of @arrival as the moment at which the train ends its movement and gets to a halt at the parent <ocpTT>.
<TT:times> (Arrival time at first OCP) TT:015 2019-06-19 2022-06-02 Arrival times at the common operating point of two consecutive <trainPart>'s of the same <train> must not contradict each other. This can be implemented either
- by only the preceding <trainPart> having arrival times while the succeeding <trainPart> does not at this operating point or
- by both <trainPart>'s having identical arrival times.


These rules apply to the arrival times in each of the specified scope's.

<TT:times> (Departure time at last OCP) TT:016 2020-10-09 2022-06-02 Departure times at the common operating point of two consecutive <trainPart>'s of the same <train> must not contradict each other. This can be implemented either
- by the preceding <trainPart> having no departure times and only the succeeding <trainPart> specifying them at this operating point or
- by both <trainPart>'s having identical departure times.


These rules apply to the departure times in each of the specified scope's.

<TT:connection> TT:017 2022-12-15 2022-12-15 If the trainPartRef attribute is given, then there must also be a trainRef attribute, and the trainPartRef attribute must point to a train part of the train referenced by the trainRef attribute.
<IS:speedChange> IS:001 2019-04-11 discarded Always define trainRelation
<IS:trackEnd> IS:002 2019-06-17
<IS:trackBegin> IS:003 2019-06-17
<IS:mileageChange> IS:006 2019-06-19
  • Define attributes @absPosIn and @absPos for "real" mileage changes
  • Define attribute @absPosIn alone in case of an ending mileage
  • Define attribute @absPos alone in case of a starting mileage
  • For starting mileages and "real" mileage changes, the @absDir has to be fiven to define the ongoing orientation of the mileage
<IS:propOperational> IS:007 2020-02-25 discarded
<IS:uptime> IS:008 2020-02-28 An <ocp> with <propOperational>@operationalType=blockSignal shall not have

@mode=manned (as a manned blockSignal shall be modelled in railML® 2.x as a blockPost).

<IS:uptime> IS:009 2020-02-28 An <ocp> with attribute <propOperational>@operationalType=stoppingPoint shall not have @mode=manned (as a stoppingPoint has no operational usage and therefore no operational staff by the IM).
<IS:uptime> IS:010 2020-02-28 An enumeration of several time periods by @from and @until for one <ocp> shall not overlap so that for every time there shall be a unique status of <uptime>.
<IS:speedChange> IS:011 2020-10-12 (date of creation of ticket 425) 2021-11-10 (40th conference slide 11) 2024-10-02 (railML.org Governance Coord approved) *Every <track> has to have at least one <speedChange> at the track begin with parameters @pos="0" and @dir="up".
  • Every <track> has to have at least one <speedChange> at the track end with parameters @pos="{value equal to trackEnd@pos}" and @dir="down".
<IS:speedProfile> IS:012 2022-03-14 @basicSpeedProfile is always linked with @influence=increasing
<IS:speedProfile> IS:013 2022-03-14
  • @influence=increasing: The <speedProfile> increases the permitted speed. If multiple "increasing" speed profiles are applicable, select the one with the highest @vMax value.
  • @influence=decreasing: The <speedProfile> decreases the permitted speed. If multiple "decreasing" speed profiles are applicable, select the one with the lowest @vMax value. If this value is lower than the speed of an "increasing" speed profile, it overrides that speed.
<IS:tunnel> IS:014 2022-03-14 Define the tunnel resistance factor @resistanceFactorPassenger resp. @resistanceFactorFreight only if @kind and @crossSection are not known.
<IS:ocp> IS:015 2022-07-14 2022-08-11 When specifying @parentOcpRef for an <ocp> circles are not allowed. That means that when following the chain of @parentOcpRef no <ocp> shall be visited twice.
<TT:times> TT:020 2024-11-21 No two attributes //<times>/@scope of the same enclosing stop/pass elements shall have the same value.
<TT:specialService> TT:021 2025-02-13 Within the same enclosing element, a date must not be contained in more than one <specialService> element.
<TT:specialService> TT:022 2025-02-13 The values of @singleDate, @startDate and @endDate of <specialService> must not be outside of the time period defined in the related <operatingPeriod>.
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