From Gary...
-----Original Message----- From: Gary Mazz [mailto:garymazzaferro@gmail.com] Hi Gyula Thank you for the formal request for the POX format. We appreciate the though and time time you spent on the proposal. I would like to clarify aspects of the XHTML5 documentation. 1) RDFa is an ontology format intended to represent knowledge domains compatible with XHTML5 documents. 2) Through careful selection of element attributes we are minimizing the overlap between HTML rendering and OCCI entity relationships. 3) Overlap of OCCI/HTML attributes are limited to defining entity instances, relationships between entities and referential information including links to URIs and document fragment references. 4) Although the initial example shows close coupling between HTML representations and OCCI constructs, we are separating RDFa from the HTML5 document constructs. We will be recommending practices to seamlessly display RDFa information using some lightweight javascript. This approach provides adopters with 4 advantages, 1) it enables providers that would like to represent OCCI information in a way appropriate for their brand, form and function. 2) it eases the burden on machines parsing semantics not interested in the visual components of the document. 3) It allows all OCCI information to reside on a single document if desired 4) It eases the requirements on current RDFa parsing technologies. I believe this approach is more closely aligned with your goals. Your feedback is welcome. I've been privately experimenting with different approaches and evaluating different RFDa toolkits to support OCCI. At this point in time, a conservative approach seems the more reliable path to enterprise application of OCCI. cheers, gary mazz Gyula Csom Gyula wrote:
Hi!
After analyzing the issue I kindly ask you to consider POX as an official OCCI representation format. Namely in order to have a programmatic interface that is easy to implement and maintain we (as a potential OCCI user) request a domain specific and extensible XML representation format.
## 1./ Features --- We request a POX representation format that 1. is domain specific, strongly typed, and free from other domains, and 2. is extensible, supports user defined elements and/or attributes.
1. The scheme has its own XML namespace and 2. is free from XML elements of orthogonal domains (like GUI, eg. XHTML) 3. Different kind of OCCI entities (compute, network, storage) are mapped to individual XML schema elements. 4. Different entity attributes are mapped to either individual XML (sub)elements or attributes (though we prefer the former, eg. attributes as XML subelements). 5. This also applies to links, and 6. actions eg. just as attributes they are handled in a strongly typed manner rather than in a generic way. 7. The scheme is extensibe (depending on the design decision under 4, it supports either the XSD any element or the anyAttribute or both).
## 2./ Intentions --- We need a programmatic interface that is easy to implement and maintain:
1. It builds upon technologies that are in common practice. We do not consider HTTP Header format to meet this criteria. XML, REST seem to be the common hypermedia format in the REST world and especially within the Cloud API space [2]. Bottom line: REST itself seems to support/encourage multiple formats. Thus I do not say that using HTTP Header is not RESTful, I just say that it doesn't seem to be a common REST format. 2. It supports separation of concerns. Being a programmatic interface, it at least separates "busines" logic (eg. data and methods) from UI (eg. user interaction). We do not consider the upcoming X/HTML+RDFa format to meet this criteria. We've found 2 issues with the format - one is trivial, the second is less trivial: 1. X/HTML intends to be a user interaction language, and RDFa to be a data annotion language for foreign markups (typically? for UI markups). Thus the upcoming format intermixes UI and data in its roots. 2. X/HTML elements and RDFa attributes are strongly coupled. Depending on the host (eg. X/HTML) structure the same RDFa sequence can result in different data structures. Thus an agent must be aware of the UI structure in order to build the data structure it is interested in. According to my preliminary examination this primarily effects recursive data structures [3] but may effect other data structures, too. Meanwhile OCCI seems to already have such structures, since categories might have child categories. Also OCCI may want to support more complex entities later (like services, and service groups which are again recursive in their nature).
One more thing. XML and JSON seems to be equally prefered by cloud providers [2]. We simply made our decision based upon the selected CMS platform: OpenNebula. It currently supports POX.
We will likely refine our request based upon feedbacks, so comments and criticism are welcome!
Kind regards, Gyula Csom
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[1] Scheme samples: request.xml, response.xml illustrate the scheme (strongly typed elements, with user defined extensions). It tries to model a new compute request.
[2] Existing Cloud APIs and formats
* OpenNebula OCCI API: REST + POX (http://www.opennebula.org/documentation:rel1.4:occiug) * Amazon EC2 API: SOAP * ElasticHosts API: REST + Plain text, or JSON (http://www.elastichosts.com/cloud-hosting/api) * IBM WebSphere CloudBurst API: REST + JSON (http://www.ibm.com/developerworks/websphere/techjournal/0911_amrhein/0911_am...) * Sun Cloud API: REST + JSON (http://kenai.com/projects/suncloudapis/pages/Home) * RedHat delta cloud API: REST + POX, and custom formats (http://deltacloud.org/api.html)
[3] RDFa samples: foaf.html, extract.rb illustrate strong coupling between X/HTML and RDFa, eg. the same RDFa sequence can result in different data structures. The foaf.html is the sample file, extract.rb is a simple Ruby script that extracts data into turtle, NT and XML formats. Builds upon the rdf_context lib (http://github.com/gkellogg/rdf_context).
[4] About our project: Our customer, the National Information Infrustructure Institute (http://www.niif.hu/en) wants to provide public cloud services for the Hungarian academic sector, and use a private cloud for its own purposes. The project is the initial step in this direction. At the technical side generally we are interested in an open, future-proof solution, especially OpenNebula as the cloud platform, and OCCI as the cloud interface.
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String coupling between XHTML and RDFa
Illustrates strong coupling between X/HTML and RDFa, eg. the same RDFa sequence can result in different data structures.
1st RDFa sequence
Alice
knows
and likes music.
2nd RDFa sequence
As we said
Alice
knows
Bob <http://example.com/bob> who also likes music.
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