Comparison of serialization or graph representation formats

[Joseph Boyle]

This is to help understand formats discussed in today's XDI2 call so we can proceed further with design of formats. Corrections encouraged.

Existing description: display format

Suggested description: display format statement serialization

Current documentation: https://wiki.oasis-open.org/xdi/XdiAbnf  (we have been conflating it with the graph rather than documenting it as a serialization)

Low level data format: proprietary

Graph serialization approach: as list of statements (triples) containing full paths

Subject/context format: Composed as bare string; always required

Predicate format: Composed as bare string separated by /

Object format: Composed as as bare string or as JSON value

Repetition elimination: none, always use full addresses

Idempotence: Sequence of operations where result in graph can be overwritten by a following statement

Minimal example: 10 bytes

=s/=p/=o<LF>

Existing description: (original) JSON serialization

Suggested description: JSON S/P or S+P statement serialization      (pronounced just as SP)

Current documentation: https://wiki.oasis-open.org/xdi/JSONSerializationRules  (will move to its own page)

Low level data format: JSON

Graph serialization approach: as list statements (triples) containing full paths

Subject/context format: Composed as JSON string along with predicate

Predicate format: Composed as JSON string along with subject

Object format: Composed as JSON string

Repetition elimination: Can omit S/P if both exactly the same

Idempotence: Sequence of operations where result in graph can be overwritten by a following statement

Minimal example: 16 bytes

{"=s/=p":["=o"]}

Existing description: parse tree serialization

Suggested description: JSON parsed statement serialization

Current documentation: https://wiki.oasis-open.org/xdi/JSONSerializationRules/Discussion 2013-04-06 entry  (will move to its own page)

Low level data format: JSON

Graph serialization approach: as list of statements (triples) containing full paths

Subject/context format: Decomposed as JSON key per context symbol and JSON string value per corresponding identifier

Predicate format: Decomposed as JSON key per context symbol and JSON string value per corresponding identifier

Object format: Decomposed as JSON key per context symbol and JSON string value per corresponding identifier

Repetition elimination: None currently

Idempotence: Sequence of operations where result in graph can be overwritten by a following statement

Minimal example: 35 bytes

[[[{"=":"s"},{"=":"p"},{"=":"o"}]]]

Existing description: graph tree serialization

Suggested description: JSON context tree serialization

Current documentation: https://wiki.oasis-open.org/xdi/GraphTreeSerialization  (will move to its own page)

Low level data format: JSON

Graph serialization approach: Nodes and contextual arcs serialized as JSON tree structure. Relational and literal arcs as keys on subject node.

Subject/context format: Decomposed as JSON key per arc, key string contains both context symbol corresponding identifier

Predicate format: Composed as single JSON string

Object format: Composed as single JSON strong except if object is an inner graph; then inner graph's subject is decomposed.

Repetition elimination: All shared prefixes among all subjects are merged as part of tree; but no such merging for predicate and object. No separate definitions needed for contexts.

Idempotence: Represents state, not a sequence of operations

Minimal example: 26 bytes

{"=s":{"/":{"=p":["=o"]}}} 

Existing description: XDI2 JSON format to represent XDI graph in Zephyr datastore:

Current documentation: https://github.com/projectdanube/xdi2-zephyr/tree/master/src/main/java/xdi2/core/impl/zephyr

Low level data format: JSON

Graph serialization approach: List of nodes each containing list of outgoing arcs and incoming arcs (please correct and improve)

Subject/context format: composed as single JSON string, but encoded as URL

Predicate format: single JSON string?

Object format: single JSON string?

Idempotence: Represents state, not a sequence of operations

Minimal example: add here