MidPoint Metadata Examples

Last modified 12 Mar 2021 10:22 +01:00

Following examples illustrate how metadata can be used in midPoint.

Metadata model definition:

model midpoint {
    metadata StorageMetadata {  // Creates type StorageMetadata
        target {
            // apply this metadata for all Prism items
            itemType prism:Item;
        }
        itemName: storage;
        item creation { ... }
        item modification { ... }
    }
}

model custom {
    // Model loaded in runtime
    namespace "http://example.com/...";
    metadata CustomMetadata {
        target {
            // We do not want this here. How to avoid it?
            itemType prism:Item;
        }
        itemName: custom;
        item foo { ... }
    }
}

Metadata serialized with data:

XML, full namespaces

    ...
    <description>
        <axiom:value>Lorem ipsum dolor sit amet ...</axiom:value>
        <axiom:metadata>
            <midpoint:storage>
                <midpoint:creation>...</midpoint:creation>
                <midpoint:modification>...</midpoint:modification>
            </midpoint:storage>
            <ex:custom>
                <ex:foo>...</ex:foo>
            </ex:custom>
        </axiom:metadata>
    </description>
    ...

XML, minimal namespaces

    ...
    <description>
        <_value>Lorem ipsum dolor sit amet ...</_value>
        <_metadata>
            <!-- No need to specify namespace here, as storage is defined in the same namespace as is the rest of the document. -->
            <storage>
                <creation>...</creation>
                <modification>...</modification>
            </storage>
            <!-- We need namespace here to avoid conflicts with other metadata (similar rules than augmentation) -->
            <ex:custom xmlns:ex="http://example.com/...">
                <!-- Namespaces are not be strictly necessary inside storage element -->
                <foo>...</foo>
            </ex:custom>
        </_metadata>
    </description>
    ...

JSON

  ...
  "description" : {
    "@value" : "Lorem ipsum dolor sit amet ...",
    "@metadata" : {
        "storage" : {
          "creation" : ....,
          "modification" : ....
        },
        "http://example.com/...#custom" : {
          "foo" : ....
        }
    }
  }

Prism Expressions

following definition has to be corrected. Prism metadata was not yet stabilized. This is expected to happen after midPoint 4.2.

model prism {
    infra ValueExpression {
        target {
            itemType prism:Property;
        }
        itemName: expression;
        type: Expression;
    }
}

Example data with expression. prop123 is a string prism property.

XML, full namespaces

    ...
    <prop123>
        <axiom:significance>unknown</axiom:significance>
        <prism:expression>
            <midpoint:const>const123</midpoint:const>
        </prism:expression>
    </prop123>
    ...

XML, minimal namespaces

    ...
    <prop123>
        <_significance>unknown</_significance>
        <_expression>
            <const>const123</const>
        </_expression>
    </prop123>
    ...

JSON

  ...
  "prop123" : {
    "@expression" : {
      "const" : "const123"
    }
  }
  ...

Question: Do we need to set @significance=unknown here explicitly? Or can we infer that from the fact that there is no @value here? We could perhaps do that in JSON. But XML will still need either explicit significance or xsi:nil, because all XMl elements have value (even if it is empty string). Or can be have XML parsing mode where we ignore whitespace in indent and consider empty string to be null?

Metadata Of Negative Values

Metadata serialized with data:

XML, full namespace

    ...
    <description>
        <axiom:value>This was all wrong, it is gone now</axiom:value>
        <axiom:significance>negative</axiom:significance>
        <axiom:metadata>
            <midpoint:transformation>
                <midpoint:mapping>...</midpoint:mapping>
            </midpoint:storage>
        </axiom:metadata>
    </description>
    ...

XML, minimal namespace

    ...
    <description>
        <_value>This was all wrong, it is gone now</_value>
        <_significance>negative</_significance>
        <_metadata>
            <midpoint:transformation>
                <mapping>...</mapping>
            </midpoint:storage>
        </_metadata>
    </description>
    ...

JSON

  ...
  "description" : {
    "@value" : "This was all wrong, it is gone now",
    "@significance" : "negative",
    "@metadata" : {
        "http://.../midpoint#transformation" : {
          "mapping" : ....,
      }
    }
  }

Notes

Considered Option: Metadata Definition using Augmentation

Not a good option. Metadata may be too complex to be handled by simple augmentation. This is also not very readable.

model midpoint {
    augmentation ValueMetadata {
        target axiom:ValueMetadata;  // Magic type
        item storage {
            type StorageMetadata;
        }
    }

    type StorageMetadata {
        item creation { ... }
        item modification { ... }
    }
}

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