How does a service description relate to a service level agreement?

See Formal Arrangements - Service Level Agreements.

The conformance checking for our service was by self-assessment. Is this correct? Is there a role for governance? What about supervisory authorities?

The conformance to the specifications is done by self-assessment. National supervisory authorities may be involved. EUROCONTROL is not involved.

How do I show compliance with Common Project 1 (CP1)?

The SESAR Deployment Programme (SDP) talks about the need for “concrete requirements that the service needs to fulfill to comply with”. The SWIM requirements are then detailed in a dedicated section (p130). This section is a good start for a compliance checklist but remember that the national supervisory authorities may have different requirements. It states:  

Related links

• SESAR Deployment Programme: https://www.sesardeploymentmanager.eu/publications/deployment-programme/
• EUROCONTROL SWIM Specifications: https://reference.swim.aero/resources.html
• Service definitions: /wiki/spaces/SCOI/pages/59605116
• SWIM Registry: https://eur-registry.swim.aero/home 

How do I record the use of GRIB2 in my service?

This best practice covers how to detail the use of e.g. GRIB2 in the service description.

SWIM-SERV-260 Service interface protocols and data format

The selection of protocol and data format for this requirement must be consistent with the interface service binding selected in SWIM-SERV-250 SWIM TI Profile and interface bindings.

The selection is found in the TIYP Specification (see diagrams below).

• WS-Light
  • no specific data format is required by the TIYP specification
• WS-SOAP
  • the service has to support XML (SWIM-TIYP-0029)
    • this applies to the messages that are exchanged by the service.
    • it is possible for the XML formatted message to embed a file.
    • SWIM-TIYP-0033 gives the content that can be embedded (e.g., as multipart files) based around MIME type.

"serviceInformationDescription": {
...
 "exchangeSchema": [
  {
   "name": "GRIB2",
   "schemaLanguage": "coverage",
   "reference": "reference to GRIB2 standard."
  }
 ]
...
}

"serviceInterface": [
 {
  "interfaceBindingDescription": "XML requests and replies. GRIB2 is embedded (as zipped files) into the reply messages.",
 }

"serviceInformationDescription": {
...
 "exchangeSchema": [
  {
   "name": "IWXXM 3.0",
   "schemaLanguage": "XML",
   "reference": "https://schemas.wmo.int/iwxxm/3.0/"
  }
 ]
...
}

SWIM-SERV-290 Information definition - minimum

The requirement expects the content of the service payload to be defined. It is here that the content of the GRIB2 file e.g. turbulence should be defined. However, GRIB2 is a standard owned and defined for the MET domain, not the Aviation MET domain. Therefore it is out of scope of the AIRM. 

"informationDefinition": [
 {
  "name": "Turbulence",
  "description": "Atmospheric flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.",
  "semanticCorrespondence": "urn:aero:airm:1.0.0:LogicalModel:Subjects:Meteorology:Turbulence"
 }
],

How do I define the list of topics for use in AMQP 1.0?

The need for harmonisation/guidance on topic trees is not unique to AMQP 1.0.

The role of topics is discussed in the TIYP supporting material. See, e.g., the "Subject-based Filtering" section in https://reference.swim.aero/technical-infrastructure/guidance-for-pub-sub-push-implementation.html that discusses topic enumerations and topic trees. The getTopics operation allows a service consumer to request the list of topics that are available to use in the subscription.

The topics themselves are URIs and should be based on the data that is exchanged. The need for semantic interoperability applies to the topic names. Therefore, it a best practice to use terms coming from a common semantic reference such as the a stardardised information exchange model, the AIRM and/or the list of service categories.

An example, using terms from the AIRM and the format used in the TIYP supporting material:

• /meteorology/precipitation
• /meteorology/precipitation/LFPG

It is also best to avoid business and service logic in the topic tree such as the way in which the data is served. There is also no need to prefix the items in the topic tree with e.g. "topic/"

How do I decide on the granularity of a service?

It is difficult to provide an exact answer to this question because there are many factors that affect the granularity of the service.

Service granularity is related to the design principle of service composability which defines services in such a way that they can be used in a service composition. A service composition is an aggregation of services where many smaller (i.e. fine grained) services (the composition members) are combined together in a larger (coarse grained) service. Typically a composition member provides functionality to the other services in the service composition. An example to think of as service composition is a service that mashes up data from various domains to create integrated picture (e.g. combining aeronautical information with flight data).

The functional scope also affects the granularity of the service. It is based on the operational needs of the service consumer. The service should be meaningful in the sense that it solves a whole problem for users and it is important to understand what that problem is e.g. is it to see all of the meteorological weather products or simply METARs.

The information exposed also affects the granularity. For example, the service may have operations to allow a consumer to get all messages, get an individual message, get a property of a message or a combination of these. The decision here is also driven by operational needs and the information exchange requirements. Likewise, the format of the information can be a driver - is it preferable to have one service that provides information in many formats (e.g. IWXXM and GRIB2) or to have each format as a separate service. However, in general, a new format and/or technical protocol is introduced in a new interface within the existing service.

The decision also depends on where the service sit in the overall service oriented architecture. For example, a coarse-grained service may be exposed to a set of external consumers closer to an application/business need while microservices are exposed more transversely but also more at the heart of common functionality for all, hence also the practices around microservices.

In Europe, some services that implement information exchanges are regulated, in the sense that they are listed in the EU Regulation - Common Project 1 and in the SESAR Deployment Programme. These may act as a guide in deciding the granularity of a new service. On the other hand, the list may act as input to a wider service orientation activity.

Each of my service consumers has a dedicated endpoint. Is this described as one service with multiple endpoints or as different services?

This situation allows each service consumer to have the information customised to their needs. However, as the operational need and functionality of the service remains consistent, it is a best practice to deal with this as a single service.

The Service Metadata Schema for service descriptions makes the definition of at least an endpoint mandatory. Therefore, it is not possible to simply ignore the endpoint field. However, the schema does allow users to define multiple endpoints and you can also use parameterized URLs (to illustrate: https://www.domain.com/url?variable=value&variable=value). The use of parameterized URLs is very common and can be a sensible solution to the problem described while fitting inside the current schema restrictions. The description of the endpoint can then be used to say that the parameters will be assigned to the consumer when a formal arrangement (such as a service level agreement) is agreed.

How do I document the HTTP error codes in my service description?

My service relies on the standard HTTP error codes. Is there a need to document them in the service description?

The Examples/Notes section of requirement SWIM-SERV-220 Service behaviour explains that error messages and error handling in general can be included in a model view (as part of SWIM-SERV-330 Model view). They are modelled as part of the detailed service behaviour.

However, it is possible to add an entry in the service behaviour section of a service description. For example:

Other error messages are documented in SWIM-SERV-280 Service messages.

How is the quality of service documented at various service lifecycle stages?

How do I document quality of service in a service description?

See SWIM-SERV-180 Quality of service.

How do I document quality of service in a service definition?

A service definition sets out community agreed requirements on the service to be implemented. The community can be strict or less strict with the requirements.  Therefore, the quality of service requirements can:

• be left abstract (e.g. "The service shall achieve a quality that is sufficient to ensure the service is fit for purpose.");  or
• give a minimum to be reached by all service providers, in which case the guidance set out in SWIM-SERV-180 Quality of service for service descriptions can be applied. For example:
  • "The service shall support a capacity of at least 2000 service requests per hour."

If the requirements are left at the abstract level, implementers have freedom to define their own concrete quality of service parameters. The service description will then describe the concrete parameters.

How is the quality of data documented at various service lifecycle stages?

How do I document quality of data in a service description?

There is no requirement to document the quality of data in a service description. However, it can be added if needed and help inform the negotiations of the "formal arrangement" in a similar way to the quality of service parameters as explained at Formal Arrangements - Service Level Agreements.

SWIM-SERV-190 Source of information is used to record modifications that have happened to the information.

How do I document quality of data in a service definition?

The items used to describe quality of data vary between information domains. They may include, for example, accuracy, resolution and precision.

A service definition sets out community agreed requirements on the service to be implemented. The community can be strict or less strict with the requirements.  Therefore, the quality of data requirements can:

• be left abstract (e.g. "The information offered by the service shall achieve a quality that is sufficient to ensure the service is fit for purpose."; or
• give a minimum to be ensured by all service providers either by including requirements or making reference to them.

If the requirements are left at the abstract level, implementers have freedom to define their own concrete quality of data.

Requirements may be found in:

• ICAO documents. For example, "The data shall meet the data quality requirements outlined in the PANS-AIM Data Catalogue".
• EU regulations. For example, "The aeronautical data offered by the service shall satisfy the applicable sections of Commission Implementing Regulation (EU) 2017/373 of 1 March 2017".
• community agreed requirements such as AIXM coding guidelines