No. In OGDL egdes are represented by space and don't carry any information. On the other hand, it is nevertheless possible to define complexer graph description languages on top of OGDL.
Apart from the syntax, the underlying model is different. XML is a mark-up language, and it can represent information trees and also mixed content. The essential difference between the two is that XML can represent both data and documents, while OGDL is oriented towards data only. In XML, mark-up and data separators have only one syntax, while in OGDL only data separators are defined (as space). That said, there are other document description languages that use a different syntax for structure and mark-up, and OGDL can be used in conjunction with additional mark-up, but it remains the question if this is the best way.
OGDL is born as a very simple and readable way to structure text information. It does away with the element/attribute dicotomy existing in XML, and has very few grammar rules (productions). It is both human and machine readable, and best suited for applications where data is exposed to human interaction. OGDL files can be slightly larger or shorter than equivalent XML files, depending on the use of elements versus attributes in XML.
Both use space to structure text, but there is no other similarity. YAML is a data serialization language that supports only two complex types: maps (hashes) and lists (vectors). OGDL on the other hand, needs a different complex type, one that preserves order and can hold duplicate entries: a named list (Graph, in the APIs). While YAML could also be used for configuration files and other similar applications, its underlying memory organization is exposed in the syntax and that makes it less human friendly.
Also, YAML is complex. For more information on YAML, see yaml.org.
Yes, with the xml2ogdl utility. But OGDL cannot represent mixed content cleanly, so the conversion either drops it or represents it as is (in original XML).
It depends on the node content. In OGDL any string can be a node, while in XML not every string can be an element. If any non terminal node in the OGDL stream conforms to the XML element syntax, then a clean conversion can be made (but there is not a specific tool or emitter for XML available as of now).
Not at the moment. Types can be implemented as a layer on top of the basic syntax.
Not at the moment. It is likely that schemas will be part of OGDL in the future. Schemas and types could be integrated into a future OGDL Schema specification.
No. You loose order and duplicates. The language APIs define the Graph object for that purpose.