Applying LDP concepts to bug tracker

In this post I'll explore how some products that support bug tracking, such as Rational Team Concert, model their internal "Work Item" resource given W3C Linked Data Platform and OSLC concepts.  This will also highlight how various capabilities are needed to solve some key problems in a simple way.  I will be "paraphrasing" what the actual runtime resource will look like to help with human consumption of the examples (as the real-world ones can sometimes have additional concepts and capabilities that don't apply to the simple part of the model we are focused on here).

Let's take one of the most simple examples of what one might find, let's say a bug (aka "Defect") that has a few properties but no associated attachments or child bugs.

Representation of bug http://example.org/bugs/13:

@prefix dc:  <http://purl.org/dc/terms/> .
@prefix ocm: <http://open-services.net/ns/cm#> . 

<> a ocm:Defect ;
   dc:title "Bug in rendering large jpgs" ;
   dc:identifier "13" .

Now we'll explore how add a couple screen shots to the bug. Using this information I have with this resource, I'm not sure how I do that (assuming I am a Linked Data client). I could just attempt to PUT replace the contents and add a ocm:attachment statement referring to the screenshot. Depending on the server, it may reject it for a couple of reasons, such as: it doesn't known anything about ocm:attachment, or it has restrictions on the object (where the attachment is physically stored), or simply PUT updates not allowed for ocm:attachment.
To help with this problem, we can associate an ldp:Container with this bug resource to assist with this. So we expand our example, with out modifying any of the original model, just adding a few more statements.

@prefix dc:  <http://purl.org/dc/terms/> .
@prefix ldp: <http://w3.org/ns/ldp#> .
@prefix ocm: <http://open-services.net/ns/cm#> . 

<> a ocm:Defect ;
   dc:title "Bug in rendering large jpgs" ;
   dc:identifier "13" .

<attachments> a ldp:Container ;
   ldp:membershipPredicate ocm:attachment ;
   ldp:membershipSubject <>.

This tells my client now that we have an ldp:Container associated with the bug, since the ldp:membershipSubject connects this container to the bug. I can inspect also ldp:membershipPredicate to know for which same-subject and same-predicate pairing I can use this container to assist with managing and navigating them.
Now I have a URL http://examples.org/bugs/13/attachments where I can POST a screenshot to create an attachment and associate it with bug 13. Let's look at what the POST looks like:

Request:

POST http://example.com/bugs/13/attachments
Slug: screenshot1.png
Content-Type: image/png
Content-Length: 18124

[binary content]

Response:

HTTP/1.1 201 CREATED
Location: http://example.com/bugs/13/attachments/3
Content-Length: 0

Now that the attachment has been created, we can fetch bug 13 again to see what we have.

@prefix dc:  <http://purl.org/dc/terms/> .
@prefix ldp: <http://w3.org/ns/ldp#> .
@prefix ocm: <http://open-services.net/ns/cm#> . 

<> a ocm:Defect ;
   dc:title "Bug in rendering large jpgs" ;
   dc:identifier "13" ;
   ocm:attachment <attachments/3> .

<attachments> a ldp:Container ;
   ldp:membershipPredicate ocm:attachment ;
   ldp:membershipSubject <>.

We now see that there is an ocm:attachment statement associated with bug 13. This statement was added by the server when it processed the POST request to create a new resource (attachment) and then added it as a member of the attachments associated with the bug.
We can also see that this list can grow to be quite large. Experience has shown, that end users of bug trackers need to attach a number of documents, images, logs, etc. with bugs. This need also comes from a number of other capabilities such as having nested bugs or tasks. To illustrate, let's assume our bug tracking server has been upgrade or now exposes children resource within bug resources (or has had children added by other means). Let's take a look at bug 13 again:

@prefix dc:  <http://purl.org/dc/terms/> .
@prefix ldp: <http://w3.org/ns/ldp#> .
@prefix ocm: <http://open-services.net/ns/cm#> . 

<> a ocm:Defect ;
   dc:title "Bug in rendering large jpgs" ;
   dc:identifier "13" ;
   ocm:attachment <attachments/3>, <attachments/14> .
   ocm:child <../47>, <../2> .

<attachments> a ldp:Container ;
   dc:title "Attachment container for bug 13" ;
   ldp:membershipPredicate ocm:attachment ;
   ldp:membershipSubject <>.

<children> a ldp:Container ;
   dc:title "Children for bug 13" ;
   ldp:membershipPredicate ocm:child ;
   ldp:membershipSubject <>.

As you can see, the bug model stays very simple with statements about bug 13 being made directly about it using simple RDF concepts where the statements are of the form [bug13, predicate, object|literal]. We can repeat this pattern and use it in many other forms, such as a container of all the bugs the serve knows about, which I plan to illustrate in other posts.
Disclaimer: some of the predicates used in these examples show they are in the OSLC-CM namespace but have not been approved by the WG. This was done just for simple illustration.

Making progress towards an OSLC-CM 3.0

Been a while I have talked about a specific domain working group and what has been going on.  Though the work for a post-2.0 Change Management specification has been evolving for some time, it is coming along nicely.  I've been focusing much of my energy on getting the core-est part of Core (W3C Linked Data Platform and Core 3.0) rolling, while keeping an eye and hand involved with CM.

To summarize the OSLC-CM WG has looked at a number of prioritized scenarios:

• IDE Task federation and management
• Transitioning states
• Programmatically accessing and uploading attachments
• Querying across multiple states in a single request
• Additional semantics on regards to priority, severity and additional types of resources

We currently have draft specification text for most of the scenarios above.  We are planning to enter into convergence soon and start to do some implementation to validate the specifications.

Special thanks to Sam Padgett for leading the OSLC-CM efforts, planning meetings, keeping minutes, keeping track of issues and pushing forward with the draft specification.  Looking forward to getting some of these approaches implemented and specification wrapped up.

Trip Report from EclipseCon 2013

I had a chance, along with Michael Fiedler,  to attend the US EclipseCon 2013 in Boston, MA in late March.   In addition to presenting a BOF and a session on OSLC, Linked Data and Lyo, we were able to attend several sessions, panel discussions and BOFs.   It was also a great chance to meet with members of the OSLC and Lyo communities to discuss the challenges of tool integration.

General Impressions from the Conference

It was cool to see and hear OSLC and Eclipse Lyo in a variety of sessions.  There were good active discussions with the Eclipse Mylyn team regarding their recent m4 proposal, including how OSLC and Lyo play a key part.  It was good to explore ways we could work together with Mylyn, Orion, Hudson and more.  We did do a lot of education and exploration with a number of attendees that had no or limited knowledge of what was going on within OSLC and Lyo.  Various panels, keynotes and sessions often called out the need for tool vendors to be able to collaborate on open interfaces....we asked them: "have you heard of OSLC?"  There were a number of people making the case for OSLC-based integrations very easy.

Here is a summary of the two sessions we presented at EclipseCon:

1) Lifecycle Tool Integrations: Linked Data, OSLC and Eclipse Lyo
Session type: Birds of a Feather

The participants ranged from experienced OSLC implementers interested in contributing to Eclipse Lyo to those new to OSLC looking for learning resources. 

The discussion covered the re-vamped tutorial on open-services.net, using the Lyo OSLC4J Bugzilla adapter as a learning resource and some general OSLC and linked data integration philosophies.  Topics included:

• a description of an OSLC4J implementation in progress which exposes EMF Models as OSLC resources - being considered for contribution to Lyo
• the experiences of a developer who has implemented several OSLC integrations to enable tools to participate in an ALM system
• The OSLC CM 1.0 integrations developed for the Mantis bug tracker and FusionForge
• Status of Eclipse Lyo - what is new in 1.1 and what is coming
• One OSLC implementer strongly recommended developing integrations using 2.0 of OSLC.  He also pointed out authentication is a primary painpoint for the work he has done.

2) Leveraging W3C Linked Data, OSLC, and Open Source for Loosely Coupled Application Integrations
Session type: ALM Connect track

EclipseCon 2013 Learn and share about integrations using Eclipse Lyo, OSLC and Linked Data from sspeiche

This session was a 35 minute tour through tool integration, problems with previous approaches and new approaches using linked data and OSLC.

This was followed by an overview of open source projects relevant to this space (Jena, Wink, Clerezza, Lyo etc) and a brief demo of some potential integrations between Eclipse Orion and a Change Management tool (Bugzilla) and an Automation tool (Lyo automation reference implementation).   

There was very little time left for questions at the end, but there were some good ones which pushed the session into overtime: 

• Interest in the concept of delegated UIs and the responsibilities of the tool hosting them - described the OSLC concepts in some detail
• Interest in the concept of UI previews and compact representations.   How these resources can be used to link to full representations was described.
• Some clarifying questions were raised by a few folks about the details of the Bugzilla integration demonstrated.   Explained it is the live Eclipse Bugzilla instance, but that it could have been any OSLC CM provider.

Special thanks to Michael Fiedler for both authoring some of this content of this blog post, as well as building the demo, presenting and too many things to list here.

W3C Linked Data Platform WG 2nd Face to Face meeting March 13-15 Boston

I just returned from the 2nd face to face meeting for the W3C Linked Data Platform (LDP) working group located at MIT in Cambridge, MA. There were about 14 attendees in all, a good number but perhaps low for a WG that has 50 total registered. Being the 2nd face to face meeting of a relatively new working group, meant this was the first meeting where we could dig in our heals and start tackling issues. We reviewed our deliveries: a must deliverable of the spec and a number of supporting documents: use case and requirements, access control guidance, possible primer, deployment guide (need a better name) and test suite.

We prioritized the issues we wanted to discuss early on the first day to make sure we got all the "big hitter" issues out on the table. I added to this list some of the key OSLC items such as binary resources and metadata, patch and more. One thing we learned as we got into the next day, there still was some confusion on the model. I surfaced ISSUE-59 to hopefully help simplify the model.

Here are the detailed meeting minutes from: day 1, day 2 and day 3.

Some of the key issues discussed were:

ISSUE-15 Sharing binary resources and metadata
The WG came to the following resolution after much discussion about concerns of different behavior of POST'ing RDF formats which create LDP-Rs and which response location headers should used.

Resolution: Assuming the existing qualifications that POST is optional, and supporting "binary" media types is optional: The expected response to a post for create that creates a non-LDPR is a 201, with location header whose URI I identifies the resource whose representation matches the POST input, and the response SHOULD include a Link header rel="meta" href= another URI P identifying the resource whose state is the server-managed properties. The URIs I and P MAY be distinct, but this is not required. When the object of a membership triple (I) is DELETEd, the server MUST automatically deletes any related resource P that it created previously

ISSUE-17 Recommended PATCH document (and 27 & 45) 

There were a number of PATCH related issues, like 27 whether POST could be used to tunnel PATCH but WG decided just to use PATCH. Also there is 45, which suggested the need to use POST'ing of RDF formats to LDP-Rs to append/add to existing resources. The WG decided that this would be fairly different than what is done with POSTing to LDP-Cs which creates a new resource and adds membership triples, plus we have a solution to append by using PATCH-insert. For 17, the original proposal was to use the Talis changeset format but due to a variety of reason this was withdrawn (don't recall the problems with Talis changeset). Instead the WG decided to pursue its own simple PATCH document that leveraged existing quad formats such as TriG. The WG has an action to define the minimal and work with issues and proposals to expand on it.

Other issues we discussed were on our list to watch as of course the resolution could impact us but the issues listed were not identified by OSLC community members as a high priority.  Overall it was very encouraging to see the WG make progress on such key issues.  It is also a little disappointing we didn't make more progress in other areas.  It is most likely that we won't enter into "Last Call" until after our 3rd face to face which is being planned for mid-June.

OSLC's relationship with Semantic Web technologies

The technical basis for accessing data through OSLC has its roots in Linked Data, which has its origins with Semantic Web technologies.  Some worry about the costs of supporting this for some simple integration scenarios, though OSLC only depends on a small amount of it.  For those that bought into the full stack of Semantic Web technologies for various domain solutions realize there is tremendous value in what it can provide but that it also comes at some cost.  The cost is in aspects of Semantic Web such as reasoners, inferencing, search engines, RDF and specialized repositories for dealing with these things.

OSLC takes a minimal incremental approach to depend on only what is needed to satisfy the integration scenarios.  So far that has led us to leverage a simple standard way of describing resources using RDF.  That is about where the Semantic Web technology dependency ends.  We leverage a few terms out of RDF Schema to help with defining our own vocabulary terms but do not go beyond that as it might imply that clients would need to process inference rules against the resource representations they receive to learn more.

Since a primary goal of OSLC is to not reinvent but leverage standards based approaches that meet our requirements, I can see cases where it might be good to adopt some more Semantic Web technologies.  Though to be clear, for tools to get value out of OSLC-based integrations, only some RDF syntax readers and writers are needed.  There is no need for tools to have be rehost or rewrite them onto a new technology base, they can simple adapt their solution with a simple fasade or update their existing REST APIs to provide this support.

W3C Linked Data Platform WG -- 1st Face to Face Meeting

I recently attended the 2012 W3C Technical Plenary / Advisory Committee (TPAC) in Lyon, France from October 29 to November 2.

RDF WG: Monday and Tuesday 

I attended the RDF F2F Working Group face to face meeting as an observer since I'm not an member of that WG though of course interested in a number of topics.  The RDF working group is nearing the end of its charter (Jan 2013) and making good progress on a number of its deliverables such as Turtle, JSON, TriG, n-triple, n-quad serialization formats.  There are a number of key issues that are of great interest such as ISSUE-77 marking rdf:Seq as archaic (this if particular interest to work at OSLC). There was a breakthrough in direction with named graphs by resolving to not define detailed semantics on identification of graphs, instead just allowing simply names/labels for graphs.

RDF WG Minutes: Day 1 and Day 2

TPAC Plenary Day: Wednesday

Jeff Jaffe CEO of W3C kicked off the day with a brief keynote and then logistics for breakout sessions.

I attended these sessions:

• Social Web: lots of interest in linked data and social web.
• Government Linked Data: discussion and update on work going on with existing WG, there is need for some guidelines and have need for LDP work
• Linked Data for Web Developers: a fair amount of discussion around JSON, including a "white-boarding" session by Tim Berners-Lee talking about some approaches using JSON.  There was also discussion of a need for some schema-like need for RDF data, which I explained we have similar need and have some experience with OSLC Resource Shapes.

Linked Data Platform (LDP): Thursday and Friday 

Of course this was the primary reason I was here.  Agenda covered a range of topics as it was our first face to face meeting. Discussed Use Case and Requirements, Primer, Test Suite, Implementations, next F2F and of course spec issues.  Tim Berners-Lee attended both days and was very active in discussing the issues, he had strong views on how some of LDP should be shaped.

Probably the biggest change is the resolution around ISSUE-25 where the ldp:Container follows strong composition model instead of weaker aggregation.  There was discussion for a common set of needs around paging and ordering of contents.

LDP WG Minutes: Day 1 and Day 2

Overall Impressions

It is clear there are many W3C members that are very passionate and believers of Linked Data, including Tim Berners-Lee.  Discussions with many shown they are interested in keeping LDP simple and willing to jump in and add support to their products early.

Trip Report from JavaOne 2012

Trip Report: JavaOne 2012 October 1-4, San Francisco 

I attended my first JavaOne conference, where I presented and attended a number of sessions and events.

Leveraging W3C Linked Data for Loosely Coupled Application Integrations

Tuesday Oct 2, 8:30

Track: Enterprise Service Architectures and the Cloud

There were about 90 people who preregistered for the session (see attachment) but seemed like there was a bit less than that at the actual session (50). Since they don’t serve the free coffee until after the 8:30 sessions, I felt like the attendees seemed very engaged by their responses and didn’t see anyone sleeping. The best was at the end where I had about 10 people approach me. Someone stated he was from a major news media company who asked how they could get involved in W3C Linked Data Platform (LDP) work and I highlighted some work at BBC that he might be interested in as well. Also a development manager from automative sector, asked how they could get involved as he was very interested in requirements traceability. Good news was that I could connect him with what other efforts in automative that were already occurring. There were a few others from healthcare and life sciences sector that said they were interested as well, handing out my card to a number of folks.

Linking the Java Application Lifecycle with Hudson

Wednesday Oct 3 4:30

Track: Development Tools

I was not on the original agenda to speak here but Mik Kersten CEO of Tasktop asked that I join him to explain Linked Data and OSLC, and give an overview of current activities. This session was also co-presented by Gregory Stachnick, Oracle Senior Director, Product Management. Greg is responsible for Oracle’s Eclipse-based tools strategy. Good overall flow considering some late changes, story around linking the lifecycle and need for standard integrations was good.

Some other activities:

Tuesday night Eclipse community meetup, good to talk with some Eclipse community members and talk about Lyo futures.

A number of sessions on JAX-RS, REST, WebSockets, Cloud, NoSQL, Hudson, CI, e4, ...

It was interesting to see the overall interest in REST, WebSockets, NoSQL and big data.

Overall very useful trip, look forward to trying to get back in 2013.