i. Abstract

TimeseriesML 1.2 defines an XML encoding that implements the OGC Timeseries Profile of Observations and Measurements, with the intent of allowing the exchange of such data sets across information systems. Through the use of existing OGC standards, it aims at being an interoperable exchange format that may be re-used to address a range of data exchange requirements.

ii. Keywords

The following are keywords to be used by search engines and document catalogues.

ogcdoc, OGC document, Timeseries, Observations, Exchange, Interoperability, TimeseriesML, XML, GML

iii.          Preface

This standard is an XML implementation of the conceptual model defined in OGC Timeseries Profile of Observations and Measurements. This standard has been developed from work initially undertaken within OGC WaterML 2.0: Part 1 – Timeseries.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The Open Geospatial Consortium shall not be held responsible for identifying any or all such patent rights.

Recipients of this document are requested to submit, with their comments, notification of any relevant patent claims or other intellectual property rights of which they may be aware that might be infringed by any implementation of the standard set forth in this document, and to provide supporting documentation.

iv.          Security Considerations

No security considerations have been made for this standard

v.          Submitting organizations

The following organizations submitted this Document to the Open Geospatial Consortium (OGC):

• Australian Bureau of Meteorology
• Met Office
• Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO)
• Landcare Research
• Météo-France
• KISTERS AG
• Environment Canada
• US National Weather Service

vi.          Submitters

All questions regarding this submission should be directed to the editor or the submitters:

1.    Scope

This document is an OGC® Implementation Standard for the representation of the Timeseries Profile of Observations and Measurements as XML. TimeseriesML 1.2 is implemented as an application schema of the Geography Markup Language version 3.3, making use of the OGC Observations & Measurements standards. TimeseriesML 1.2 is designed as an extensible schema to allow encoding of data to be used in a variety of exchange scenarios. Example areas of usage are: cross-border exchange of observational data; release of data for public dissemination; enhancing disaster management through data exchange; and exchange in support of national reporting. The core aspect of the Timeseries Profile of Observations and Measurements is the correct, precise description of timeseries. This document defines an implementation of this profile.

2.    Conformance

This standard defines an XML encoding standard for the OGC Timeseries Profile of Observations and Measurements.

Conformance with this standard shall be checked using all the relevant tests specified in Annex A (normative) of this document. The framework, concepts, and methodology for testing, and the criteria to be achieved to claim conformance are specified in the OGC Compliance Testing Policies and Procedures and the OGC Compliance Testing web site^[1].

In order to conform to this OGC^®interface standard, a software implementation shall choose to implement:

a)     Any one of the conformance levels specified in Annex A (normative).

All requirements-classes and conformance-classes described in this document are owned by the standard(s) identified.

3.    References

The following normative documents contain provisions that, through reference in this text, constitute provisions of this document. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the normative document referred to applies.

OGC 15-043r3 – Timeseries Profile of Observations and Measurements

OGC 08-131r3 – The Specification Model – A Standard for Modular Specification

ISO 19103:2005 – Conceptual Schema Language

ISO 19108:2002 -Geographic information - Temporal schema

ISO 19109:2005 -Geographic information – Rules for application schema

ISO 8601- Data elements and interchange formats – Information interchange – Representation of dates and times

OGC 10-004r3 OGC Abstract Specification Topic 20 – Observations and Measurements (aka ISO 19156:2011)

OGC 08-015r2 OGC Abstract Specification Topic 2 – Spatial Referencing by Coordinates (aka ISO 19111:2007)

OGC 07-011 OGC Abstract Specification Topic 6 – Schema for Coverage geometry and functions (aka ISO 19123:2005)

OGC 01-111 OGC Abstract Specification Topic 11 – Geographic information — Metadata (aka ISO 19115:2003)

ISO: ISO 19115:2003, Geographic information — Metadata, 2003

OGC 07-036 Geography Markup Language (aka ISO 19136:2007)

OGC 09-146r2 Implementation Schema for Coverages (1.0.1)

OGC 10-126r4 OGC WaterML2.0 part 1 – Timeseries.

OGC 08-094r1 OGC SWE Common Data Model Encoding Standard v2.0

The UCUM Organization: Unified Code for Units of Measure (UCUM) – Version 1.8, July 2009

OGM: Unified Modeling Language (UML). Version 2.3. May 2010.

W3C: Extensible Markup Language (XML) – Version 1.0 (Fourth Edition), August 2006

W3C: XML Schema – Version 1.0 (Second Edition), October 2004

4. Terms and Definitions

This document uses the terms defined in Sub-clause 5.3 of [OGC 06-121r8], which is based on the ISO/IEC Directives, Part 2, Rules for the structure and drafting of International Standards. In particular, the word “shall” (not “must”) is the verb form used to indicate a requirement to be strictly followed to conform to this standard.

For the purpose of this document, the following additional terms and definitions apply:

4.1 Coverage

Feature that acts as a function to return values from its range for any direct position within its spatial, temporal or spatiotemporal domain

[ISO 19123:2005, definition 4.17]

4.2 Domain Feature

Feature of a type defined within a particular application domain

[ISO 19156, definition 4.4]

4.3 Feature

Abstraction of real-world phenomena

[ISO 19101:2002, definition 4.11]

4.4 Observation

Act of observing a property

[ISO 19156, definition 4.10]

4.5 Observation Procedure

Method, algorithm or instrument, or system of these which may be used in making an observation

[ISO 19156, definition 4.11]

4.6 Property <General Feature Model>

Facet or attribute of an object referenced by a name

EXAMPLE: Abby’s car has the color red where “color red” is a property of the car instance

4.7 Sampling Feature

Feature, such as a station, transect, section or specimen, which is involved in making observations concerning a domain feature

[ISO 19156, definition 4.16]

4.8 Sensor

Type of observation procedure that provides the estimated value of an observed property at its output

Note: A sensor uses a combination of physical, chemical or biological means in order to estimate the underlying observed property. At the end of the measuring chain electronic devices often produce signals to be processed

[OGC SWE Common 2.0, definition 4.5.]

4.9 Timeseries

A sequence of data values which are ordered in time. The sequence typically records (or predicts) the value of a property of a feature over a time interval, with interim values at times within the interval. These times are monotonic and are often, but not always, at regular intervals (e.g. an hourly timeseries).

5. Conventions

5.1 Abbreviated Terms

In this document the following abbreviations and acronyms are used or introduced:

GMLCOV OGC Implementation Schema for Coverages

ISO International Organization for Standardization

O&M Observations and Measurements

OGC Open Geospatial Consortium

SensorML Sensor Model Language

SWE Sensor Web Enablement

TSML TimeseriesML

TVP Time-Value Pair

UML Unified Modeling Language

UTC Coordinated Universal Time

5.2    UML Notation

The diagrams that appear in this standard are presented using the Unified Modeling Language (UML) static structure diagram.

Note: Within the context of this profile, the following color scheme is used to identify the package in which the class exists. This is just for informative purposes.

Blue: Defined within the Timeseries Profile of O&M (conceptual model)

Yellow: Defined within this standard (XML implementation model)

Green: ISO19156 – Observations & Measurements

Red: Other (ISO or GML)

5.3    Finding Requirements and Recommendations

This standard is identified as http://www.opengis.net/spec/timeseriesml/1.2. For clarity, each normative statement in this standard is in one and only one place and defined within a requirements class table and identified with a URI, whose root is the specification URI. In this standard, all requirements are associated to tests in the abstract test suite in Annex A using the URL of the requirement as the reference identifier.

Requirements classes are separated into their own clauses and named and specified according to inheritance (direct dependencies). The Conformance test classes in the test suite are similarly named to establish an explicit and mnemonic link between requirements classes and conformance test classes.

6.    XML Implementation (normative)

In addition to the UML conceptual model this standard defines a GML XML Schema implementation that is compliant to the UML conceptual model. The XML Schemas for this implementation are published at:

http://schemas.opengis.net/tsml/1.2/

Schematron patterns are implemented for some requirements where appropriate and are published at the same location.

6.1    XML encoding principles

The following principles apply to data encoded according to the TimeseriesML 1.2 XML schema.

6.1.1    Conformance to GML 3.3 encoding rules for codelists

This XML Schema implementation imports the OGC GML 3.2.1 schemas. However, codelists are implemented according to the clarified rules for codelists in the OGC GML 3.3 specification. Namely that items in codelists are referred to using gml:ReferenceType and not encoded with gml:CodeType.

None of the GML 3.3 schema types are used in this implementation and therefore only GML 3.2.1 schemas are imported by the TimeseriesML 1.2 XML schemas. This is consistent with the note in the GML 3.3 specification which reads: A GML application schema conforming to this standard will import the GML 3.2 schema plus zero or more additional GML 3.3 schemas as needed.

6.1.2    Extends the OGC Implementation Schema for Coverages

The TimeseriesML schema supports both an interleaved time-value pair encoding and a domain, range encoding. The domain, range encoding inherits from the coverage schema defined in the OGC Implementation Schema for Coverages (09-146r2). The interleaved timeseries encoding is a representation of a special case of the CV_DiscreteCoverage class from OGC Abstract Specification Topic 6, in which each GeometryValuePair has a ‘geometry’ which is a timestamp, and a ‘value’ which is a measure or other simple datatype. The OGC CIS v1.1 specification provides alternative representations of coverages, including an option for interleaving coverages, which can be useful for timeseries of more complex values.

6.1.3    Virtual typing

In accordance with OMXML, the specialization of the OM_Observation result type is provided through schematron restriction. The om:type element may be used to specify the type of OM_Observation that is being encoded. This shall be done using the OGC Name URI for the corresponding type from the following table.

Likewise, a tsml:type property is present on the TimeseriesDomainRange type to enable a soft-typing approach to this class. The values for this property should be taken from Table 2.

6.1.4    Efficiency of encoding

This XML Schema implementation takes the approach that, where conceptual classes can be combined without loss of clarity, they are. For example, the same metadata classes are used for both Categorical and Measurement timeseries. This is to avoid a proliferation of similar classes in the XML encoding.

The following table outlines the mapping between the conceptual model and the XML Schema implementation.

6.1.5    Abstract requirements and conformances classes

As noted in the OGC Modular Specification section 6.2, the tests for abstract conformance classes may need to be described in the subclass classes if the base requirements classes are ambiguous for the abstract class. This is the case for the two styles of timeseries conformance classes, domain-range and interleaved (time-value pair). Some requirements for these classes are re-specified in more concrete terms to allow more explicit testing.

6.2    XML Examples

XML examples are published alongside the XML schemas at http://schemas.opengis.net/tsml/1.2/. In all examples, the following namespaces are used.

6.3    Requirements Class: XML Rules

6.3.1    Requirements class overview

This requirements class contains a set of general rules applicable to the XML encoding.

6.4    Requirements Class: Timeseries Observation

6.4.1    Requirements class overview

This requirements class restricts the content model for the XML element OM_Observation relating specifically to timeseries observations. The requirements classes that depend on this class describe specific result types of time series. The restrictions rules for OM_Observation are captured in the ‘xsd-timeseries-observation.sch’ Schematron file.

6.5    Requirements Class: Timeseries (TVP) Observation

6.5.1    Requirements class overview

This requirements class captures the core type of timeseries observation – one with a result of an interleaved time-value pair timeseries. This restriction is defined in the ‘xsd-timeseries-tvp-observation.sch’ Schematron file.

6.6    Requirements Class: Categorical Timeseries (TVP) Observation

6.6.1    Requirements class overview

This requirements class restricts the type of timeseries observation to one with a result of an interleaved time-value pair timeseries where each value is a Category. This restriction is defined in the ‘xsd-categorical-timeseries-tvp-observation.sch’ Schematron file.

6.7    Requirements Class: Measurement Timeseries (TVP) Observation

6.7.1    Requirements class overview

This requirements class restricts the type of timeseries observation to one with a result of an interleaved time-value pair timeseries where each value is a Measure. This restriction is defined in the ‘xsd-measurement-timeseries-tvp-observation.sch’ Schematron file.

6.8    Requirements Class: Timeseries (Domain Range) Observation

6.8.1    Requirements class overview

This requirements class captures the domain range type of timeseries observation. This restriction is defined in the ‘xsd-timeseries-domain-range-observation.sch’ Schematron file.

6.9    Requirements Class: Categorical Timeseries (Domain Range) Observation

6.9.1    Requirements class overview

This requirements class captures the categorical domain range type of timeseries observation.

6.10    Requirements Class: Measurement Timeseries (Domain Range) Observation

6.10.1    Requirements class overview

This requirements class captures the measurement domain range type of timeseries observation.   

6.11    Requirements Class: Timeseries encoded as Time-Value Pairs

6.11.1    Requirements class overview

The Time-Value Pair (TVP) Encoding schema contains types suitable for encoding TimeSeries (both Measurement and Categorical) in a sequence of time-value pairs.

Note that this time-value pair encoding of timeseries encoding takes the name ’TimeseriesTVP’.

The domain range encoding equivalent takes the name TimeseriesDomainRange.

The complete TVP encoding of timeseries, including associated metadata classes is shown in the figure above.

6.11.2    CategoricalTVP properties

CategoricalTVP is the encoding for time-value pairs where the value is a category.

6.11.3    Measure properties

Measure is a measure implementation with an optional unit of measure (so that the unit of measure can be set to a default for the whole timeseries rather than repeating the unit for each data value).

6.11.4    MeasurementTVP properties

MeasurementTVP is the encoding for time-value pairs where the value is a measure.

6.11.5    TimeseriesTVP properties

The core class for the timeseries time-value pair encoding.

6.11.6    TimeValuePair properties

A base class for different time-value pair implementations.

6.12    Requirements Class: Categorical (TVP) Timeseries

6.12.1    Requirements class overview

This requirements class restricts the value type of each time-value pair to be a Category.   

6.13    Requirements Class: Measurement (TVP) Timeseries

6.13.1    Requirements class overview

This requirements class restricts the value type of each time-value pair to be a Measure.   

6.14    Requirements Class: Timeseries encoded as Domain Range

6.14.1    Requirements class overview

The Domain Range Encoding schema contains types suitable for encoding TimeSeries (both Measurement and Categorical) in a domain (times), range (values) block. This schema extends the OGC GMLCov schema.

The TimeseriesDomainRange encoding extends the OGC Implementation Model for Coverages by adding bespoke metadata and annotation elements.

The class TimeseriesDomainRange is used for all domain range encodings. It extends the GMLCov DiscreteCoverage with a timeseries metadata extension.

6.14.2    TimeseriesMetadataExtension properties

TimeseriesMetadataExtension enables use of TimeseriesML metadata classes in GMLCov XML schema. The associated XML examples demonstrate how this is applied in practice.

6.14.3    AnnotationCoverage properties

An annotation coverage can be used to apply metadata to individual points in the timeseries.

Informative note: In the XML Schema the AnnotationCoverage is a specialization of the gmlcov:AbstractDiscreteGoverage XML Schema type. This standard is not otherwise prescriptive about the content of the AnnotationCoverage beyond that specified in the OGC Coverages Implementation Model, but it could be used to provide a value array or list of comments or other values as in the two examples below.

<tsml:AnnotationCoverage gml:id="quality_cov">
<gml:domainSet xlink:href="#temporal_domain"/>
<gml:rangeSet>
<gml:CategoryList codeSpace=“http://opengis.net/def/waterml/2.0/quality/”>good bad good missing good bad</gml:CategoryList>
</gml:rangeSet>
<gmlcov:rangeType/>
</tsml:AnnotationCoverage>
 
<tsml:AnnotationCoverage gml:id="comment_cov">
<gml:domainSet xlink:href="#temporal_domain"/>
<gml:rangeSet>
<gml:ValueArray gml:id="comment_array">
<gml:valueComponents>
<gml:Category>This is a free text comment</gml:Category>
<gml:Category xsi:nil=“true”/>
<gml:Category>Example comment</gml:Category>
<gml:Category>Another one</gml:Category>
<gml:Category>Has to be one for each point</gml:Category>
</gml:valueComponents>
</gml:ValueArray>
</gml:rangeSet>
<gmlcov:rangeType/>
</tsml:AnnotationCoverage>

6.14.4    TimeseriesDomainRange properties

The TimeseriesDomainRange element extends the OGC coverage model with metadata extensions for timeseries data. The metadata classes are the same as for the time-value pair encoding.

6.15    Requirements Class: Collection

6.15.1    Requirements class overview

The Collection schema contains a collection element as well as other document specific types.

The XML Schema implementation of Collection maps closely to the conceptual model. The key implementation points to note are that all observationMembers are implemented by OM_Observation, and that ConformanceClass is implemented as a reference (xlink:href) from DocumentMetadata.

6.15.1.1    Collection properties

TimeseriesML defines a generic collection feature type, Collection, to allow the grouping of observations and/or sampling features with metadata to describe the nature of the collection. Such collections are required in a number of data exchange scenarios; whether the underlying transport technology is web services, FTP or other technologies.

6.15.1.2    SamplingFeatureMember properties

A sampling feature member may be either a single sampling feature (e.g. MonitoringFeature) or a group of features (SF_SamplingFeatureCollection). This is a Union class.

6.16    Requirements Class: MonitoringFeature

6.16.1    Requirements class overview

The Monitoring Feature schema contains the definition of the Monitoring Feature type that is the (sampling) feature of interest of a TimeSeries observation.