yEd does not display your data values because the sample document you posted is not valid (yEd) GraphML.
To understand how yEd expects meta data in GraphML files,
- create a new diagram in yEd,
- create a custom property for nodes (see "Edit" -> "Manage Custom Properties"),
- add one node and
- select the new node,
- specify a value for the node's custom property (see section "Data" in the properties view in yEd's lower right corner),
- save your diagram to GraphML, and finally
- inspect the GraphML in a text editor or an XML editor.