docs: add decision record about IDS filtering

docs/developer/decision-records/2022-09-18-ids-catalog-request-filtering/README.md

@@ -0,0 +1,47 @@
+# Add filtering to IDS catalog requests
+
+## Decision
+
+Extend existing `CatalogRequest` object with list of criteria used to filter `Assets` within `Catalog` response.
+
+## Rationale
+
+In a large scale environment, with multiple EDCs holding the information about hundreds of thousands of `Assets`, instead of 
+looping thought all of the `ContractOffers`, there is a need to narrow the results down to even single offer. For example, an 
+`Asset` might hold the 'special' type of data (like registry or database) and should be searchable by its type.
+
+## Approach
+
+As the logic for querying `AssetIndex` by `QuerySpec` is already in place, all we have to do is to pass filtering criteria via IDS Api:
+
+
+`filter` property has to be added to the IDS message:
+
+```
+// in MultiPartCatalogDescriptionRequestSender.java
+message.setProperty(CatalogRequest.FILTER, request.getFilter());
+```
+
+Then, on the receiving end, it's simply extracted:
+
+```
+// in DescriptionRequestHandler.java 
+var querySpec = ofNullable(message.getProperties().get(CatalogRequest.FILTER))
+    .map(map -> objectMapper.convertValue(map, typeRef))
+    .orElse(/*should never occur!!*/)
+```
+
+Existing `ContractOfferQuery` will be used to transport both `Range` and filtering criteria to lower layers.
+
+And now, they can be applied to `AssetIndex` search query when constructing the `Catalog` response:
+
+1) pass Criterions to the `CatalogServiceImpl.getDataCatalog()`
+2) attach to the existing `ContractOfferQuery` object
+3) in `ContractOfferServiceImpl.queryContractOffers()`, merge with `AssetSelectorExpressions` from contract definitions.
+
+## Considerations and limitations
+
+- there is no standardized query language nor will there be one for the foreseeable future;
+- querying is based on the "Canonical format": (https://github.com/eclipse-dataspaceconnector/DataSpaceConnector/blob/main/docs/developer/sql_queries.md),
+  i.e. the schema of the queried objects, i.e. their Java class. That implies that the client must have knowledge of the schema; 
+- that schema is subject to change without special notice.

docs/developer/decision-records/README.md

@@ -36,3 +36,4 @@
 - [2022-08-09 Project structure review](2022-08-09-project-structure-review/)
 - [2022-08-11 Versioning and Artifacts](2022-08-11-versioning_and_artifacts/)
 - [2022-08-17 Remove H2 Database Tests](2022-08-17-remove_h2_database_tests/)
+- [2022-09-18 IDS catalog request filtering](2022-09-18-ids-catalog-request-filtering/)