Update model.md

* Splitting to not-normative and normative part
* adding  description on registry

model/model.md

@@ -6,6 +6,11 @@ The following sections outline the Dataspace Information Model, which form the f
 
 ### 2.1 Dataspace Entity Relationships
 
+#### 2.1.1 Context of the Dataspace Protocol
+
+In a broader context, the Dataspace Protocol enables the interaction between participants of
+a Dataspace. This may require addiotonal concepts, which are not in scope of this specification.
+The definitions below are therefore informative and not-normative.
 The relationships between the primary [Dataspace](./terminology.md#dataspace) entities are defined as follows:
 
 ![](./m.dataspace.relationships.png)
@@ -14,10 +19,18 @@ Note that all relationships are multiplicities unless specified.
 
 - A [Dataspace Authority](./terminology.md#dataspace-authority) manages one or more [Dataspaces](./terminology.md#dataspace). This will include [Participant](./terminology.md#participant) registration and may entail mandating business and/or technical requirements. For example, a [Dataspace Authority](./terminology.md#dataspace-authority) may require [Participants](./terminology.md#participant) to obtain some form of business certification. A [Dataspace Authority](./terminology.md#dataspace-authority) may also impose technical requirements such as support for the technical enforcement of specific usage policies.
 - A [Participant](./terminology.md#participant) is a member of one or more [Dataspaces](./terminology.md#dataspace). A [Participant](./terminology.md#participant) registers [Participant Agents](./terminology.md#participant-agent) that perform tasks on its behalf.
+- A `Dataspace Registry` manages the registered `Participant Agents` in a `Dataspace`. Registration and unregistration processes may be different depending on various aspects.
 - A [Participant Agent](./terminology.md#participant-agent) performs tasks such as publishing a [Catalog](./terminology.md#catalog) or engaging in a [Transfer Process](./terminology.md#transfer-process). In order to accomplish these tasks, a [Participant Agent](./terminology.md#participant-agent) may use a _**verifiable presentation**_ generated from a _**credential**_ obtained from a third-party [Credential Issuer](./terminology.md#credential-issuer). A [Participant Agent](./terminology.md#participant-agent) may also use an _**ID token**_ issued by a third-party [Identity Provider](./terminology.md#identity-provider). Note that a [Participant Agent](./terminology.md#participant-agent) is a logical construct and does not necessarily correspond to a single runtime process.
 - An [Identity Provider](./terminology.md#identity-provider) is a trust anchor that generates `ID tokens` used to verify the identity of a [Participant Agent](./terminology.md#participant-agent). Multiple identity providers may operate in a [Dataspace](./terminology.md#dataspace). The types and semantics of ID tokens are not part of this specification. An [Identity Provider](./terminology.md#identity-provider) may be a third-party or a [Participant](./terminology.md#participant) itself (for example, in the case of decentralized identifiers).
 - A [Credential Issuer](./terminology.md#credential-issuer) issues _verifiable credentials_ used by [Participant Agents](./terminology.md#participant-agent) to allow access to [Datasets](./terminology.md#dataset) and verify usage control.
 
+Further information on the context of the Dataspace Protocol can be found in the [IDSA Rulebook](https://docs.internationaldataspaces.org/idsa-rulebook).
+
+#### 2.1.2 Dataspace Protocol specific
+
+The Dataspace Protocol shall enable the interactions between the `ParticipantAgents` in a Dataspace.
+The following concepts are therefore normative.
+
 The diagram below depicts the relationships between [Participant Agent](./terminology.md#participant-agent) types:
 
 ![](./m.participant.entities.png)