BC: [XML] schema: convert simple nested-elements to attributes

[jkowalleck]

Have things attributes, instead of child elements,
if they are simple and describe the entity/element and don't need to be contained.

from things like this

<workflow>
  <task>
    <uid>fsdkfjklsdf<uid>
    <name>my task<name>
    <startDate>2020-07-10T15:00:00Z</startDate>
    <endDate>2020-07-10T16:00:00Z</endDate>
    <command>ls -lisah .</command>
    <command>rm -rf foo</command>
  <task>
<workflow>

to this like this

<workflow>
  <task uid="fsdkfjklsdf"
        name="my task"
        startDate="2020-07-10T15:00:00Z"
        startDate="2020-07-10T16:00:00Z"
>
    <command>ls -lisah .</command>
    <command>rm -rf foo</command>
  <task>
<workflow>

benefits of attributes over elements:

• i could write XPATH queries easily for an element based on some attribute. selecting on a child-element with a certain content is hard
• said XPATH could be used in XSD's key and keyref and unique constraints and rules.
• said XPATH could be used by downstream consumers of a BOM xml, if they want to query the document.

examples:

• i could query one/all BOM documents ad find all tasks that have a dateDiff of started-to-done-interval of more than 10 minutes,
  instead of jumping to :parent here and there (if it was possible with nested-elements at all)

PS: you guys told me it was hard for you to get an idea what should be an attribute in XML and what a nested element, as you are more used to JSON and YAML.
maybe this helps to get the right idea:

• if you write a property in JSON schema, then it is an attribute in XML, not a nested element.
• If you write an array JSON schema, then the elements should be nested in XML, not attributes.