update guidance linked_standards and add link to OC4IDS identifiers g…

…uidance

docs/guidance/map/linked_standards.md

@@ -8,7 +8,7 @@ The [Open Contracting for Infrastructure Data Standards](https://standard.open-c
 
 A joint effort by the [Infrastructure Transparency Initiative](https://infrastructuretransparency.org) (CoST) and the Open Contracting Partnership, it builds on best practice in open data and openness of public infrastructure procurement globally.
 
-The [Project](https://extensions.open-contracting.org/en/extensions/project/master/) extension describes how to connect OCDS and OC4IDS datasets.
+OCDS and OC4IDS data sets ought to be linked using the `planning.project` field, referencing the OC4IDS project identifier in `planning.project.id`.
 
 ## Open Fiscal Data Package
 

docs/schema/reference.md

@@ -150,6 +150,8 @@ The planning section is used in a planning process. This includes information ab
 
 Apart from documents, the majority of planning information is held within the budget block. This is designed to allow both machine-readable linkable data about budgets, cross-referencing to data held in other standards such as the [Fiscal Data Package](https://specs.frictionlessdata.io/fiscal-data-package/) or [International Aid Transparency Initiative Standard](https://iatistandard.org/en/), and human readable description of the related budgets and projects, supporting users to understand the relationship of the contracting (or planning) process to existing projects and budgets even where linked data is not available.
 
+The `planning.budget.projectID` field should not be used to disclose the identifier of an infrastructure or PPP project. Rather, this field is used to disclose the identifier of a programme of work as it appears in a budget, like a national or state budget. Since such programmes of work can include many infrastructure projects, it is necessary to disclose their identifiers separately. Use the the `planning.project.id` field to disclose the identifier of an infrastructure or PPP project.
+
 ````{admonition} Example
 :class: hint
 
@@ -170,7 +172,9 @@ Apart from documents, the majority of planning information is held within the bu
 
 #### Project
 
-The `planning` object includes details of the infrastructure or public-private partnership (PPP) project to which a planning process is related. The identifier of the project ought to be disclosed in `planning.project.id`. This object is designed to allow both machine-readable linkable data about the parent project, cross-referencing to data held in other standards such as the [Open Contracting for Infrastructure Data Standards Toolkit (OC4IDS)](https://standard.open-contracting.org/infrastructure/latest/en/projects/#what-is-a-project) and the [OCDS for PPPs](https://standard.open-contracting.org/profiles/ppp/latest/en/) profile, and human readable description of the parent project, supporting users to understand the relationship of the contracting (or planning) process to their parent project even where linked data is not available.
+The `project` object includes details of the infrastructure or public-private partnership (PPP) project to which a planning process is related. This object is designed to allow both machine-readable linkable data about the parent project, cross-referencing to data held in other standards such as the [Open Contracting for Infrastructure Data Standards Toolkit (OC4IDS)](https://standard.open-contracting.org/infrastructure/latest/en/projects/#what-is-a-project) and the [OCDS for PPPs](https://standard.open-contracting.org/profiles/ppp/latest/en/) profile, and human readable description of the parent project, supporting users to understand the relationship of the contracting (or planning) process to their parent project even where linked data is not available.
+
+Where there is a separate OC4IDS dataset that describes the project the identifier from this dataset should be referenced in `project.id`. Where there is not a separate project dataset an appropriate project identifier will need to be generated. For more information on project identifiers see [OC4IDS Project Identifiers](https://standard.open-contracting.org/infrastructure/latest/en/guidance/identifiers/).
 
 ````{admonition} Example
 :class: hint