Using metadata:type and metadata:null attributes within an metadata:value element feels odd, and we already use a local attribute "type" for the metadata:annotation element, so I defined the metadata:value element with local attributes "type" and "null":

<!-- payload format for property value responses -->
<xs:element name="value">
<xs:complexType mixed="true">
<xs:sequence>
<xs:any namespace="http://docs.oasis-open.org/odata/ns/data" processContents="lax" minOccurs="0"
maxOccurs="unbounded" />
</xs:sequence>
<xs:attribute name="type" type="edm:TPropertyType" />
<xs:attribute name="null" type="xs:boolean" />
</xs:complexType>
</xs:element>

Looking at how collections of primitive or complex scalar values are now represented, it feels extremely odd that the "element" element is "defined" in the (probably forever) schema-less "data" namespace instead of also being defined in the metadata namespace like its siblings metadata:annotation and metadata:value.

I'm concerned about the application of this issue also changing the attributes to the default namespace.

I think it's useful to have a common way to read the nullability and type of a property, regardless of the name of the property.

btw; putting "element" in the data namespace was a mistake that we should fix. as ralph says, it should be in the metadata namespace, only user data should be in the data namespace.

I propose
1) We keep null and type in the metadata namespace
2) We fix a historical error by putting element (always) in the metadata namespace.

Should we also remove the type attribute from the annotation element? Currently it's a local attribute there.

What about data:links and data:uri used for representing LinkUrls (section 12)?
ODATA-276 already suggests replacing data:uri with metadata:entity-ref, so it would seem logical to replace data:links with metadata:entity-refs or metadata:entity-references.

I could go either way for the annotation element; the code knows it's reading an annotation, rather than a property, so it likely has different code anyway, but it is convenient to have one way to get the type so is probably easier to make it metadata:type.

Yes, if we reject ODATA-276 we should put uri and links in the metadata namespace as well, and if we do approve ODATA-276 we should put links (or whatever we call it; I kinda like "entity-references") in the metadata namespace.

How do we express that an annotation has anull value?

<m:annotation term="some.term" />

or

<m:annotation term="some.term" m:null="true" />

Omitting the annotation isn't sufficient if the metadata document defines a "default" value for that term.

Right; we would want to do <m:annotation term="some.term" m:null="true" />.

Note that:
-new example in 5.1.11.1 uses m: rather than metadata: in example
-also, previous example uses m:type rather than metadata:type
-also, two instances in 5.4, Delta Response example (mea culpa)