Data lookup

A certain group of functions takes a map/dictionary as argument: <lookup>, <whitelist>, <blacklist> etc. In this section the usage of such maps will be explained. We start with a simple example of data lookup.

Local Lookup

Take for instance an operation in which you want to replace values according to a lookup table: Value 'A' maps to 'print', 'B' maps to 'audiovisual' an so forth. This is accomplished by the <lookup> function. The lookup table is defined inside the <lookup> tag. The following code snippet depicts this situation.

<data source="[email protected]" name="dcterms:format">
  <substring start="0" end="1" />
  <lookup>
    <entry name="A" value="print" />
    <entry name="B" value="audiovisual" />
    <entry name="O" value="online" />
  </lookup>
</data>	

Maps

The same lookup tables may used in different places in a Metamorph definition. To enable reuse, a map/dictionary can be defined separately from the respective lookup function. In the following listing the <lookup> function refers to the table using the name material. Later in the code the actual map is defined using the <map> tag. See listing \ref{maps}.

[...]
<lookup in="material">
[...]
<map name="material">
  <entry name="A" value="print" />
  <entry name="B" value="audiovisual" />
  <entry name="O" value="online" />
</map>

External Data Sources

The situation might arise that the data used in lookup operations cannot be hardcoded in xml; or at least hard-coding it would be inconvenient. Imagine we want to resolve author ids to author names: Putting all the id-name mappings into the Metamorph definition file is certainly not desirable. To address this issue, any data source implementing the Map interface can be connected to the Metamorph object as shown in the following code snippet. The data is referenced in the Metamorph definition file by 'name of map'.

//create a Map. Any object implementing Map<String, String> will do
final Map<String, String> map = new HashMap<String, String>();
map.put("one key", "first String");
map.put("another key", "another String");

//tell metamorph to use it during lookup operations
metamorph.putMap("name of map", map);