VOSpace 2.0 Proposed Recommendation: Request for Comments

This document will act as RFC centre for the IVOA VOSpace 2.0 Proposed Recommendation. The latest version of the specification (02-Dec-2011) can be found at:

VOSpace is the IVOA interface to distributed storage. This specification presents the first RESTful version of the interface, which is functionally equivalent to the SOAP-based VOSpace 1.15 specification . Note that all prior VOSpace (1.x) clients will not work with this new version of the interface.

Reference Interoperable Implementations

The following are known implementations of VOSpace 2.0:

Implementations Validators

(If any, indicate here the links to Implementations Validators)

RFC Review Period: 20-May-2012 to 22-Jun-2012

TCG Review Period: TCG_start_date - TCG_end_date

Comments from the IVOA Community during RFC period: 20-May-2012 to 22-Jun-2012

In order to add a comment to the document, please edit this page and add your comment to the list below in the format used for the example (include your Wiki Name so that authors can contact you for further information). When the author(s) of the document have considered the comment, they will provide a response after the comment.

Additional discussion about any of the comments or responses can be conducted on the GWS VOSpace mailing list (vospace@ivoa.net). However, please be sure to enter your initial comments here for full consideration in any future revisions of this document

Comment by NormanGray

Sect.2 mentions that VOSpace URIs may have fragments, and illustrates how a fragment is literally copied into the retrieval URL from the vos: URL. However this is the only mention of 'fragment' in the document. If the intention is that the VOSpace spec regards the path+query+fragment as opaque, then it would be useful to state this explicitly in Sect.2. Given the potential problems with fragments (see Urbana TCG slides and draft uri-fragments note) it might be useful to do one of the following:

  • forbid fragments in VOSpace URIs;
  • require that any # characters in a VOSpace URI are encoded when being transformed into a retrieval URL; or
  • specify that any fragment is removed as part of the process of transforming the VOSpace URI into the retrieval URI, on the grounds that the fragment will (or at least should) be automatically removed, in passing, by the library which does the HTTP retrieval.

Editorial remark: the HTML version is served with MIME type text/html; charset=UTF-8 (the meta@http-equiv element in the HTML header is ignored), but the content is ISO-8859-1, and there are two soft hyphens (0xad) in the Sect 2 example identifier which appear wrongly in a browser which pays attention to the MIME type.

The example given is: vos://org.astrogrid.cam!vospace/container-6/siap-out-1.vot?foo=bar#baz. I agree that this is ambiguous and could be misinterpreted as identifying a node rather than referring to something internal to a data object. For example., vos://nvo.caltech!vospace/mydata/table1#row3 refers to "row3" within the data resource vos://nvo.caltech!vospace/mydata/table1 (and only resolved by the client when table1 has been retrieved) and should not the identify the data object "row3" in its own right. I will amend the text to correctly describe the behaviour (option 3 above) in the next version. -- MatthewGraham - 21 May 2012

Comments by DaveMorris

Changes to node type
Lots of places say "this operation cannot be used to change the node type".

Is there a mechanism where we can change the node type ?

What is the use case for this? It does not make sense in most cases, e.g., changing a ContainerNode to any other type. -- MatthewGraham - 25 May 2012

Multi-value properties
Section 3.2.1 states

"When a Property can take multiple values, e.g., a list of groups which can access a particular resource, these SHALL be represented as a comma-separated list."

Why SHALL and not MAY ?

Unless there is a specific reason for making this explicit, can't we leave it up to the defintion of the property type.

Some property type MAY be comma separated, most probably will, but why do we need to explicitly exclude everything else.

General principle - restrict as little as necessary, and only when we have a specific reason.

The issue of multiple valued parameters was discussed at a previous Interop and it was decided to represent these as a CSV list. Allowing arbitrary delimiters would mean that you would have to check for this information on a per space basis and it was just simpler to specify the delimiter from the outset. -- MatthewGraham - 25 May 2012

When the issue of multiple valued parameters was raised, it was suggested that they COULD be represented as a CSV list. I don't remember it being decided that they SHOULD.

The delimiter used in a particular property would be defined in the definition of the property type, identified by the property type URI, not on a per space basis.

A client only needs to check what the delimiter is IF it intends to do something with the value. Which implies that it already understands what that type of property contains, so it will know what the delimiter is.

e.g. "This property is a comma separated list of intensity values"

An application that understands the VOSpace property for "a list of intensity values" will know that the list will be comma separated.

An application that does not understand the VOSpace property for "a list of intensity values" will just treat the whole thing as a string.

If we only allow a specific delimiter, then anyone with existing tab, space, colon or other delimited data will have to re format their data to meet the specification, or they will avoid adding any detail and just define everything as opaque strings.

e.g. Java classpath

"This property is a list of files formatted using the Java classpath rules (colon or semi-colon delimited)"

is more informative than

"This property is an application specific string"

which is what will happen if we try to force people to use a tool that doesn't fit their data.

What do we gain by specifying the delimiter ?

Suggested compromise - change the spec to say

"multiple values SHOULD be comma separated, unless the property description defines a specific delimiter"

-- DaveMorris - 28 May 2012

Standard properties
Are the standard properties listed in section actually registered somewhere ?

If so, is there a queryable registry where we can access the definitions ?

The wording of the specification "The following URIs SHALL be used .." imples that these properties are part of the VOSpace 2.0 standard. In which case, these properties, and their data types, should be defined in an appendix.

As part of the standardization process, the properties will be registered using the StandardsRegExt in the Registry of Registries (i.e., under the ivoa.net namespace). I agree about an appendix and will add it to the next version. -- MatthewGraham - 25 May 2012

Soft hyphens
There are more than two soft hyphens (0xad) in the text. They appear as <?> symbols in a web browser, but sometimes they are not displayed at all in the PDF version.

They show up in some of the XML examples

and in the example identifiers

  • vos://nvo.caltech!vospace/myresults/siapout1.vot
  • vos://nvo.caltech!vospace/myresults/siap?out?1.vot
  • vos://nvo.caltech!vospace/myresults/siap-out-1.vot

I'll make the appropriate edits in the next version. -- MatthewGraham - 25 May 2012

Typo property in identifier
In section 3.2.4 Standard properties, the last property identifier

  • ivo://ivoa.net/vospace/core@btime

should probably be

  • ivo://ivoa.net/vospace/core#btime

I'll make the appropriate edit in the next version. -- MatthewGraham - 25 May 2012

Typos in compliance matrix
In appendix B: Compliance matrix

Property definition 13

  • 13 A Property has elements:uri, endpoint and param

should probably be

  • 13 A Property has elements:uri, value and optional readonly flag

If we have

  • 16 Standard capabilities are represented by the specified URIs

then should we also have

  • xx Standard properties are represented by the specified URIs

Property definition 26

  • 26 A Protocol has elements: uri, endpoint< and param

should probably be

  • 26 A Protocol has elements: uri, endpoint and param

-- DaveMorris - 23 May 2012

I'll make the appropriate edits in the next version. -- MatthewGraham - 25 May 2012


This topic: IVOA > WebHome > IvoaGridAndWebServices > VOSpace2RFC
Topic revision: r9 - 2012-05-28 - DaveMorris
 
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