Add pagination and filter changes (#228)

* Add pagination and filter changes

* Change continuation tokens

catalog/catalog.binding.https.md

@@ -60,7 +60,7 @@ Authorization: ...
 
 - The `Authorization` header is optional if the [Catalog Service](../model/terminology.md#catalog-service) does not require authorization. If present, the contents of the `Authorization` header are detailed in the [Authorization section](#13-authorization).
 
-- The `filter` property is optional. If present, the `filter` property can contain an implementation-specific filter expression or query to be executed as part of the [Catalog](../model/terminology.md#catalog) request.
+- The `filter` property is optional. If present, the `filter` property can contain an implementation-specific filter expression or query to be executed as part of the [Catalog](../model/terminology.md#catalog) request. If a filter expression is not supported by an implementation, it must return a HTTP 400 (Bad Request) response.
 
 ##### Response
 
@@ -100,10 +100,13 @@ If the request is successful, the [Catalog Service](../model/terminology.md#cata
 
 ### 3.2 Pagination
 
-A [Catalog Service](../model/terminology.md#catalog-service) may paginate the results of a [Catalog Request Message](./catalog.protocol.md#21-catalog-request-message). Pagination data is specified using [Web Linking](https://datatracker.ietf.org/doc/html/rfc5988) and the HTTP `Link` header. The `Link` header will contain URLs for navigating to previous and subsequent results. The following request sequence demonstrates pagination:
+A [Catalog Service](../model/terminology.md#catalog-service) may paginate the results of a [Catalog Request Message](./catalog.protocol.md#21-catalog-request-message). Pagination data must be specified using [Web Linking](https://datatracker.ietf.org/doc/html/rfc5988) and the HTTP `Link` header. The `Link` header will contain URLs for navigating to previous and subsequent results. Only the `next` and `previous` link relation types must be supported. 
+Note that the content and structure of the link query parameters is not defined by the current specification. 
+
+The following request sequence demonstrates pagination:
 
 ```http request
-Link: <https://provider.com/catalog?page=2&per_page=100>; rel="next"
+Link: <https://provider.com/catalog?continuationToken=f59892315ac44de8ab4bdc9014502d52>; rel="next"
 
 {
   "@context":  "https://w3id.org/dspace/v0.8/context.json",
@@ -115,8 +118,8 @@ Link: <https://provider.com/catalog?page=2&per_page=100>; rel="next"
 Second page response:
 
 ```http request
-Link: <https://provider.com/catalog?page=1&per_page=100>; rel="previous"
-Link: <https://provider.com/catalog?page=3&per_page=100>; rel="next"
+Link: <https://provider.com/catalog?continuationToken=a59779015bn44de8ab4bfc9014502d53>; rel="previous"
+Link: <https://provider.com/catalog?continuationToken=f59892315ac44de8ab4bdc9014502d52>; rel="next"
 
 {
    "@type": "dcat:Catalog",
@@ -127,7 +130,7 @@ Link: <https://provider.com/catalog?page=3&per_page=100>; rel="next"
 Last page response:
 
 ```http request
-Link: <https://provider.com/catalog?page=2&per_page=100>; rel="previous"
+Link: <https://provider.com/catalog?continuationToken=bn9556075bn44de8ab4bfc9014582t76>; rel="previous"
 
 {
    "@type": "dcat:Catalog",

catalog/catalog.protocol.md

@@ -101,7 +101,7 @@ All messages must be serialized in JSON-LD compact form as specified in the [JSO
 
 The Catalog Request Message is message sent by a [Consumer](../model/terminology.md#consumer) to a [Catalog Service](../model/terminology.md#catalog-service). The [Catalog Service](../model/terminology.md#catalog-service) must respond with a [Catalog](#31-ack---catalog), which is a valid instance of a [DCAT Catalog](https://www.w3.org/TR/vocab-dcat-3/#Class:Catalog).
 
-- The message may have a `filter` property which contains an implementation-specific query or filter expression type supported by the [Catalog Service](../model/terminology.md#catalog-service).
+- The message may have a `filter` property which contains an implementation-specific query or filter expression type supported by the [Catalog Service](../model/terminology.md#catalog-service). 
 
 - The [Catalog Service](../model/terminology.md#catalog-service) may require an authorization token. Details for including that token can be found in the protocol binding, e.g., [Catalog HTTPS Binding](./catalog.binding.https.md). Similarly, pagination may be defined in the protocol binding.