The XML import/export format closely follows the structures of the GOPPRR metamodeling language used by MetaEdit+, so anyone familiar with GOPPRR should have no problems understanding it. The structure is basically as below.

 1  <gxl>
 2    <graph type="WatchApplication">
 3      <slot name="Name">
 4        <value>
 5          <string>Stopwatch</string>
 6        </value>
 7      </slot>
 8      <object>...
 9      </object>
10      <binding>
11        <relationship>...</relationship>
12        <connection>
13          <role>...</role>
14          <port>...</port>
15          <object>...</object>
16        </connection>
17      </binding>
18    </graph>
19  </gxl>

The XML import/export document always starts with a <gxl> tag (line 1). Each graph is introduced with a <graph> tag (line 2): there may be several graphs in one import/export file.

The structures at the start of the <graph> tag are also found in all other GOPPRR element tags: objects, relationships, roles and ports. Lines 3 – 7 in our example XML illustrate how the properties attached to the GOPPRR elements are defined. Each property is introduced with a <slot> tag whose name attribute specifies its local name. Into the slot go an optional <property> tag referring to the property (not necessary for import), and a <value> tag. The <value> tag specifies the actual value of this property, within a tag that specifies its data type (e.g. <string> in line 5).

The graph definition then contains the objects and bindings in that particular graph. Object definitions come first and are denoted by an <object> tag (line 8). Objects specify their type and properties as defined about for Graph. Binding definitions follow the object definitions, each in its own <binding> tag (line 10). A binding definition contains definitions for its relationship (<relationship> tag, line 11) and connections (<connection> tag, line 12). There must be at least two connections in each binding. The connection definition contains the definitions for its role, port and object, denoted with their respective tags <role>, <port> and <object> (lines 13 – 15). If there is no port defined for the connection, the <port> tag is omitted.

This is the format expected for import; the exported files contain more details such as unique database object oid’s, which are ignored on import. The tags <graph>, <object>, <relationship>, <role> and <port> all have the same structure for their attributes and property slot elements. The value for a property slot can be string, int, bool, text, or then either graph, object, relationship, role or port GOPPRR element, or then seq, which contains a series of string or GOPPRR elements.