Canonical representation of a class object containing a list element in XML

Question

I see that most implementations of JAX-RS represent a class object containing a list of elements as follows (assume a class House containing a list of People)

<houses>
 <house>
 <person>
 <name>Adam</name>
 </person>
 <person>
 <name>Blake</name>
 </person>
 </house>
 <house>
 </house>
</houses>

The result above is obtained for instance from Jersey 2 JAX-RS implementation, notice Jersey creates a wrapper class "houses" around each house, however strangely it doesn't create a wrapper class around each person! I don't feel this is a correct mapping of a list, in other words I'd feel more confortable with something like this:

<houses>
 <house>
 <persons>
 <person>
 <name>Adam</name>
 </person>
 <person>
 <name>Blake</name>
 </person>
 </persons>
 </house>
 <house>
 </house>
</houses>

Is there any document explaining how an object should be correctly mapped apart from any opninion?

Answer 1

XML documents can only have a single root node, so the <houses> is necessary if you would want to serialize more than one <house>.

A <persons> element is not necessary as a node may contain any number of children with the same tag name – they can be disambiguated by position. It adds complication without adding value or structure. But such a grouping may be adequate e.g. when we have different kinds of inhabitants in our house:

<house>
 <inhabitants>
 <human>
 <name>Larry</name>
 </human>
 <human>
 <name>Guido</name>
 </human>
 <dog>
 <name>Rasmus</name>
 </dog>
 </inhabitants>
</house>

Here, <inhabitants> encodes a relation, whereas <human> and <dog> encode a type.

• dendini: Good point, however the next step I'd think of would be to user wrapper classes for consistency in every case, otherwise one would have to know each time whether a list might or might not contain elements of different types.