icg: updated definitions based on v4.1

Author: JanssenBrm

interoperability/definitions.qmd

@@ -47,35 +47,33 @@ analytics procedures to perform an application-specific processing task.
 
 For the sake of simplicity in the context of APEx, we refer to these simply as (EO) “algorithms”.
 
-### Algorithm Service Implementation
+### Application Algorithm Definition
 
-The algorithm definition refers to a representation of the algorithm modules and interfaces that can be exposed by an
-API and/or processing platform. Typically, it includes a general description of the algorithm along with detailed
+The application algorithm definition refers to a representation of the algorithm modules and interfaces that can be exposed
+by an API and/or processing platform. Typically, it includes a general description of the algorithm along with detailed
 information on its parameters, expected output, scientific method, and an overview of the different steps executed
 within the algorithm. Examples of algorithm definitions include openEO’s User Defined Processes (UDP) [@udp] and OGC
 Application Package [@ap], using the Common Workflow Language (CWL) [@cwl].
 
-### Algorithm Catalogue
+To increase uptake and interoperability, APEx aims to enable the execution of application algorithm definitions via
+standardised web service APIs. This transitions algorithms from being rather arbitrary pieces of software with potentially
+complex requirements, in terms of execution environment, usage, inputs, …, into on-demand services that can readily be
+invoked by stakeholders. This transformation primarily involves making the application algorithm definition available as
+a service on an algorithm hosting platform. The transition process into a hosted on-demand algorithm service is supported
+by the APEx Algorithm Support.
 
-The [APEx Algorithm Catalogue](https://algorithm-catalogue.apex.esa.int/) is a central register of algorithm
+An important boundary condition for hosted algorithms is that they can be executed at a predictable cost for a given set
+of inputs. This predictability allows a service user to accurately estimate and determine the cost associated with the
+execution of the final deployed service instance.
+
+### Algorithm Services Catalogue
+
+The [APEx Algorithm Services Catalogue](https://algorithm-catalogue.apex.esa.int/) is a central register of algorithm
 definitions and the corresponding algorithm service instances that can be executed on APEx-compliant algorithm hosting
 platforms. Curated by APEx, the catalogue relies on automated checks to ensure that advertised algorithms service
 instances are available and functional. Whenever a malfunction is detected, this is reported to ESA and the EO project
 consortium, allowing them to determine a proper course of action.
 
-### Hosted Algorithm
-
-To increase uptake and interoperability, APEx aims to enable the execution of algorithms via standardised web service
-APIs. This transitions algorithms from being rather arbitrary pieces of software with potentially complex requirements,
-in terms of execution environment, usage, inputs, …, into on-demand services that can readily be invoked by
-stakeholders. This transformation primarily involves converting a given algorithm into an APEx-compliant algorithm
-definition and making it available as a service on an algorithm hosting platform. The transition process into a hosted
-on-demand algorithm service is supported by the [APEx Algorithm Support](../propagation/index.qmd).
-
-An important boundary condition for hosted algorithms is that they can be executed at a predictable cost for a given set
-of inputs. This predictability allows a service user to accurately estimate and determine the cost associated with the
-execution of the final deployed service instance.
-
 ### Algorithm Hosting Platform
 
 An EO algorithm hosting platform enables the execution of a standardised algorithm, represented by an algorithm
@@ -96,6 +94,38 @@ affects properties such as cost, performance, stability, and the amount of compu
 algorithm. Compliance with these requirements does not necessarily imply a high overall quality level across all
 aspects, ensuring that EO projects retain a sufficient degree of freedom in selecting their preferred platform.
 
+### Last Mile Applications
+
+A ‘last mile’ application, as seen from the EO perspective, bridges the final gap between the user at the end of the
+value chain, and the web service APIs that offer EO-derived information. This could, for instance, be the integration
+of parcel statistics into the field management software of a farmer. In the ESA context, Green Transition Information
+Factories can be considered examples of last mile applications.
+
+Typically, each user group and domain will have its own set of purpose-built tools. The IT integrator or vendor building
+these tools will retrieve EO algorithm results via web service APIs based on open standards. These results can then be
+further processed as needed, depending on the application. Note that these applications are not necessarily EO-centric
+or even geospatial but could be using an EO algorithm as a small part or in the background.
+
+The APEx Algorithm Services Catalogue acts as a discovery tool for last mile application builders. It shows various
+technical parameters, the cost and potential limitations for specific use cases. This speeds up the discovery and selection
+process. Application builders will be required to create an account on the hosting platforms and ensure the necessary
+funds are available, if they want to test or use the API.
+
+APEx currently offers two main options for projects to develop their on-demand services:
+
+* OpenEO-based services [@openeo], implemented in line with openEO’s User Defined Processes (UDP) [@udp]
+* OGC API - Processes-based services [@apiprocess], implemented in line with the OGC Application Package Best
+Practice [@ap]
+
+These APEx-compliant technologies allow algorithms to be hosted on an APEx-compliant algorithm hosting platform and make
+them available for execution through web services. These technologies promote seamless reuse and integration of existing
+EO algorithms. Additionally, by leveraging web services and cloud-based approaches, these technologies simplify the execution
+of EO algorithms, shielding users from underlying complexities, such as data access, data processing optimisation, and other
+technical challenges.
+
+APEx remains committed to future innovation and is open to integrating additional specifications, provided they align with
+FAIR principles and facilitate algorithm execution through web services.
+
 ## Actors
 
 ### EO Project & Algorithm PI
@@ -104,9 +134,9 @@ An EO project refers to the consortium that is responsible for building the EO a
 Algorithm PI (principal investigator). In certain ESA EOP procurement and ITTs, there is now a requirement included to
 comply with APEx [Interoperability and Compliance Guidelines](../interoperability/index.md). When compliance is
 required, the consortium can utilise various services offered by APEx. Specifically, the
-[APEx Algorithm Support](../propagation/index.qmd) aims tosupport the enhancement of algorithms on a technical and
+[APEx Algorithm Support](../propagation/index.qmd) aims to support the enhancement of algorithms on a technical and
 software level and facilitate the transition to hosted algorithms that can be included in the
-[APEx Algorithm Catalogue](https://algorithm-catalogue.apex.esa.int/).
+[APEx Algorithm Services Catalogue](https://algorithm-catalogue.apex.esa.int/).
 
 ESA EO projects that do not have an explicit compliance requirement are also eligible to receive support. The APEx
 support can boost project impact, so projects are encouraged to inquire with their ESA technical officer about the