TS 26.346 FLUTE FDT Profile for 5MBS & delimiter usage

[chburdinat]

Context

5MBS uses the profiled FDT Schema from clause L.6 in TS 26.346 for the Object Distribution Method (see clause 6.2 from TS 26.517).
This profile FDT Schema reuses the delimiter element, specified in Annex J.2.

The delimiter element was introduced to ensure backward and forward compatibility for the different schema versions, according to the following mechanism:

• schemas are including extension points by using <xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>. This allows the insertion of any elements, provided they belong to another namespace:

<xs:complexType name="exampleType">
	<xs:sequence>
		<xs:element name="firstElement" type="xs:string" maxOccurs="unbounded"/>
		<xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
	</xs:sequence>
</xs:complexType>

• new elements to be inserted in the schemas are specified under a new namespace and placed at these extension points.
• To respect the Unique Particule Attribution (UPA) rule, a delimiter element separates new elements from the xs:any/ tags.

<xs:complexType name="exampleType">
	<xs:sequence>
		<xs:element name="firstElement" type="xs:string" maxOccurs="unbounded"/>
                <!--new element from a new namespace-->
                <xs:element ref="new:newElement" minOccurs="0"/>
                <xs:element ref="sv:delimiter"/>
		<xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
	</xs:sequence>
</xs:complexType>

To ensure backward compatibility, we want that a document instance, valid with the new schema, is valid as well with the old one. This is achieved by affecting delimiter to another namespace, so that new:newElement and sv:delimiter are associated to the <xs:any namespace="##other" /> of the old schema.

Description of the doubt

In L.6 of TS 26.346, there is a delimiter within the file element. It was introduced first to solve the UPA rule with the introduction of mbms2007:Cache-Control in the initial FDT schema (see 7.2.10). As Cache-Control is sharing now the same namespace in L.6, there isn’t any more issue with the UPA rule. Is there another reason to keep a mandatory delimiter element here ?

In addition, to ensure backward compatibility, the delimiter element shall be affected to another namespace.

[rjb1000]

@chburdinat is going to draft a Change Request for discussion during the joint session with 3GPP SA4 MBS on Thursday, 9th January 2025.

[rjb1000]

For reference, @tlohmar's Change Request that originally added the consolidated FDT schema in clause L.6 is here:

• TS 26.346
  • Release 17: CR0661r1 in S4-220881.

Note that this used Work Item code 5MBP3, which was a Release 17 Work Item.

Any correction will need to be made in both Release 17 (suggest 5MBP3) and mirrored into Release 18 (suggest 5MBP3, TEI18).

There is no Release 19 of TS 26.346 yet.

[rjb1000]

@chburdinat contributed a Change Request to the SA4 MBS ad hoc meeting post SA4#130:

• TS 26.346
  • Release 17: CR0670 "FDT schema corrections" in S4aI250012.
  • Release 18: Mirror CR to be drafted once the above is agreeable.

[rjb1000]

CR26346-0670 "FDT schema corrections" in S4aI250012 was endorsed today by the SA4 MBS subworking group as the way forward.

@chburdinat to revise the contribution to additionally correct the misplacement of <xs:any> in the legacy schema.