1. TS-0004 Data Representation Proposal Discussion
Group: WG3 (PRO)
Source: Peter Niblett, IBM,
Date:
Agenda: PRO#14

2. Introduction
These slides discuss approaches to resolve the issues raised in PRO-536 and PRO-537
Announced Resources
Inheritance of “Universal” and “Common attributes”
Management Resources
They do not include
Representation of Child Resource references
The question of Global vs Local element declaration

3. Announced Resources
Announced Resource Types not treated properly in current XML
Need discrete enumeration for announced Resource Types (i.e., unique values in resourceType attribute)
TS-0001 suggests that the Announced resource type takes the form <xxxxAnnc>, e.g. <ContainerAnnc>
No resource-specific XSD (yet) for announced Resource Types
Proposal
The relevant XSD files will contain Announceable and Announced versions of the resource type
We will need new short names for the announced variants
The TS-0001 statement about <xxxxAnnc> does not apply
The numeric enumeration value for resourceType of <xxxAnnc> will be 1000 more thant the value for the corresponding <xxx>

4. Attributes Following revisions to TS-0001 we now have
Five “Universal attributes”
resourceType, parentID, creationTime, lastModifiedTime, labels
Three “Common attributes” relating to Announcement
announceTo, announcedAttribute, link
It appears that only 9 resourceTypes (+ the management ones) are announceable
Four other “Common attributes”
resourceID, accessControlPolicyIDs, expirationTime, stateTag
Exceptions
stateTag is only defined for <container>, <contentInstance>, <delivery> and <request>
parentID is defined for everything except <CSEBase>
resourceID is defined for everything except <AE> and <CSEBase>
accessControlPolicyIDs is defined for everything except <accessControlPolicy>, <contentInstance> and <schedule>
expirationTime is defined for everything except <CSEBase> and <contentInstance>

5. Inheritance Model
XML Schema allows one complex type to extend another. The extension type inherits all the XML elements / attributes of its parent.
Advantages of using this mechanism to represent the universal / common attributes
Avoids having to retype the definitions into each resource
Illustrates the underlying relationship of the type definitions
When you use a tool to generate classes for an OO language (e.g. xjc to generate Java classes from an XSD) the generated classes can reflect the XML inheritance
However the exceptions listed on the previous slide make this tricky…

6. Options
Don’t use inheritance at all. Make every Resource Type declare all its attributes (universal, common, resource - specific)
Just use inheritance for the 5 universal attributes, and make the Resources declare the common + resource-specific ones
Use inheritance for both universal and common attributes. Options to make this work:
Move one or more common attributes into resource-specific section (e.g. stateTag since it is only used by 4 attributes)
Sacrifice some of the fidelity of the schemas, e.g. permit a resource schemas to include optional attributes that are not shown as present in TS-0001
Push to get further changes to TS-0001 to remove some of the irregularities
Make special cases out of some of the resources, e.g. <CSEBase>, <AE>, <accessControlPolicy>, contentInstance> and <schedule>
Construct an XML inheritance scheme to work around the irregular structure of the attributes

7. “Natural” Inheritance model
Resource used by
<CSEBase>
RegularResource used by
<delivery>
<eventConfig>
<execInstance>
<m2mServiceSubscriptionProfile>
<mgmtCmd>
<pollingChannel>
<request>
<serviceSubscribedNode>
<statsCollect>
<statsConfig>
<subscription>
AnnounceableResource used by
<accessControlPolicy>
<AE>
<container>
<contentInstance>
<group>
<locationPolicy>
<mgmtObj> specializations
<node>
<remoteCSE>
<schedule>
Assumes stateTag is moved to resource-specific
Problem resources shown in black
Note: order of attributes won’t be the same as in TS-0001

8. Problems with previous model
<CSEBase> has no parentID
Proposal: return xsi:nil
<accessControlPolicy>, <contentInstance> and <schedule> have no accessControlPolicyIDs
Proposal: special case them with a restriction to have maxOccurs = 0
<AE> has no resourceID
Proposal: define a resourceID for it in TS-0001
<contentInstance> has no expirationTime
Proposal: change TS-0001 to add it

9. Alternative Inheritance model
Assumes stateTag is moved to resource-specific
<accessControlPolicy>, <contentInstance> and <schedule> now use the xxxSubordinateResource types

10. Problems with alternative model
<CSEBase> has no parentID
Proposal: return xsi:nil
<AE> has no resourceID
Proposal: define a resourceID for it in TS-0001
<accessControlPolicy> and <schedule> have expirationTime
Proposal: change TS-0001 to add it or special case them with a restriction to have maxOccurs = 0

11. <mgmtObj>
Current schema design does not serialize attributes and child resources properly for [specializations] of <mgmtObj>
Common attributes are followed by <mgmtObj> attributes and child resources, and then specialization-specific attributes (or so-called [objectAttribute])
This could be fixed by introducing AnnouncebleManagemnt and AnnouncedManagement types
[specializations] do not have resourceType=mgmtObj in XSD
Each [specialization] is treated as a resource-specific type declaration and has a discrete element name (which is currently equivalent to resourceType)
Need resolution of this issue with WG2 and WG5.