ReqIF is the new OMG standard for requirements interchange. RIF is the predecessor to it and already supported by many tools like DOORS. RMF delivers both the standards as Ecore models. However, there are quite a few differences between the two standards making them type incompatible.
The main differences lies in,
1. Element naming.
For example, the element RIF is now called REQIF, SpecHierarchyRoot is now Specification and so on.
2. More specification types.
If you know the RIF model already, you would know the concept of SpecTypes. This element allows creation of new types. In RIF and ReqIF, SpecObjects (the instance values) and SpecRelations (relations between instances) are typed. However, in RIF, both refer to the same SpecType element, where as ReqIF has different types called SpecObjectType for SpecObject, SpecRelationType for SpecRelation and some more new types.
3. More attribute definition and value types.
RIF had only a single attribute definition type called AttributeDefinitionSimple. ReqIF extends this for different the different data types as AttributeDefinitionInteger, AttributeDefinitionReal, AttributeDefinitionString etc. Same for values as AttributeValueInteger, AttributeValueReal, AttributeValueString etc.
4. RIF XML uses no XML attributes where as ReqIF uses a lot of them.
For example, IDENTIFIER is an XML element in RIF whereas it is a XML attribute in ReqIF.
This brings us to the question – how do I convert my existing RIF files to the new ReqIF format? Considering the fact that there are a lot of industry samples in RIF format, we thought of writing a RIF to ReqIF converter. The transformer takes in a RIF file and transforms it into a ReqIF, retaining all its contents. You could also do an in-memory transformation between the two models.
This is how a RIF source than we passed to our converter looks like after transformation.
Preparing to make the initial code contribution for RMF, we ran our RIF/ReqIF metamodels through several performance tests. To start with, we tested the load and save times of RIF files based on some industry samples. To get some comparison data, we generated XMI files using the same data held in RIF XML files and tested the load/save time against it. The results are quite promising.
Before we go into the details of the tests, its better to define two components involved in our test comparisons.
- The customized RIF XML loader (a.k.a RMF Loader) and serializer (a.k.a RMF Serializer) for loading/saving OMG RIF XML files into RIF Ecore metamodel (read more on the metamodel implementation here).
- The default RIF XMI loader and serializer for loading/saving RIF XMI files into RIF Ecore model (this is not in the scope of RMF. We use this only to get some comparison).
Here are some highlights from our tests.
- A 32MB RIF XML file is loaded in 14.4 seconds by RMF loader where as the same data in XMI format is loaded by the default EMF XMI loader in 22.2 seconds (and 70 mins(!!) without any optimizations to the XMI loader)
- The average time taken to load per MB of data from RIF XML is 0.5 seconds, whereas RIF XMI takes 1.63 seconds per MB. For save, average time taken per MB of data to RIF XML is 0.09 seconds, whereas RIF XMI takes 1.22 seconds per MB
- The load and save time for RIF XML files by RMF loader/serializer increases linearly with size
RIF/ReqIF is the new OMG standard for requirements interchange. RMF (currently in proposal phase) provides an EMF Ecore based metamodel implementation for the RIF/ReqIF XML format. The metamodel is a clean implementation of the format without any “XML noise”. The Ecore metamodel also conforms to the CMOF metamodel delivered by OMG (as it has been derived from it). The metamodel reads/writes RIF/ReqIF data in conformance with the RIF/ReqIF XML Schema.
The challenge in the Ecore based RIF/ReqIF implementation was the customization of loaders and serializers to make them RIF/ReqIF XML Schema conformant. EMF provides different ways of customizing the XML output.
1. Using ExtendedMetadata annotations.
Both approaches are quite tricky to implement when the expected XML output has structural differences compared to the Ecore metamodel. For example, the XML output has wrapper elements for lists (ELists) in the Ecore metamodel.
We went in for a third approach.
We imported RIF/ReqIF XML schema using EMF importer to create a RIF/ReqIF XML Ecore model (Anyone who has done this, knows it’s an “ugly” metamodel that EMF generates here). The next step was to create the real RIF/ReqIF metamodel, by importing RIF/ReqIF CMOF file. We then wrote a generic (of course reusable) Ecore XML to Ecore converter to do a model to model transformation in both directions. The whole processing is cleanly hidden in a new EMF Resource implementation such that the user hardly knows anything about these.
The following are the advantages we saw in the approach.
1. You don’t do customizations at a XML level, but at a higher EMF model API level. That is, you don’t hack some XML SAX events, but work with familiar EMF APIs.
2. The generic Ecore converter has enough hooks to plugin in the transformations.
3. Easy maintenance as the customizations are available in one place.
The drawback of this approach could be the processing involved in the model to model transformation. However, the highly optimized model to model transformation we implemented doesn’t make it all that slow. Our performance tests proves this (which would be the topic of my next blog post). It is infact upto 300 times faster than having the same data in the default XMI format (Yes I meant 300! Ed Merks is going to get back to me on this I hope ;) )
Ed did get back to me. With the performance optimizations applied to XMIResource loader to use cache for Intrinsic Ids and URIs, the performance improved dramatically. The XMI resource loader now takes only 22,2s to load a 32MB sample, compared to the earlier 70mins. I am glad that our RIF XMLResource however takes only 14,4s for the same contents.
Over the last few months some guys at itemis and Düsseldorf University have been working closely to bring out a solution to the open in an effort to lessen the big gap we have currently in Eclipse Ecosystem in the area of Requirements Management (RM). Requirements Modeling Framework (RMF) has been proposed to Eclipse Foundation as an open source project under Model Development Tools Project.
Scope of RMF
The scope of the project, as described in the proposal, is to provide an implementation for the OMG ReqIF standard (just as the Eclipse UML2 project provides an EMF based metamodel for OMG UML). Requirements management tools could then base their implementation on the provided ReqIF metamodel. It is also in the scope of the project to deliver a requirements authoring tool, again based on the ReqIF metamodel and optionally a generic traceability solution.
Significance of ReqIF
ReqIF (Requirements Interchange Format) is an open standard from OMG for requirements exchange (I had blogged a while ago on how we arrived at ReqIF (earlier called RIF)). Many tools like DOORS already support a snapshot export to this format. Having an EMF based metamodel for ReqIF, opens up the Eclipse framework for integration and new tool development in the area of Requirements Engineering.
ReqIF in a nutshell
ReqIF offers a generic metamodel to capture requirements (The generic nature is at times highly criticized. More on that later). The figure above shows a bird’s-eye view of the metamodel. The metamodel allows creation of requirement types (SpecType) with different attributes types and also instances for it (SpecObject). Since ReqIF also carries the metadata (in the form of SpecTypes), it makes it possible for any tool that understands ReqIF to process the data.
ReqIF also allows creating hierarchy for requirements, grouping them and controlling user access. To support rich text, the metamodel reuses XHTML.
Generic nature and “meta”ness of ReqIF
Anyone expecting a requirements metamodel might be surprised at first when they have a look at ReqIF. You hardly find a term called “requirement” in there. ReqIF is more at a higher meta-level, that is M1. It has been designed this way for a reason.
Requirements Management is an evolving field and until recently never crossed company boundaries. With tighter collaboration between partner companies the benefits of applying RM across company borders became known. The field being highly dominated by commercial products gave barely any chance for standardization. A group of companies in the automotive field, realized that with such a diversity existing hardly any unification is possible. They gave birth to this generic requirements interchange format which was later adopted by OMG and standardized.
The generic structure of ReqIF allows companies to use the tools of their choice to do requirements management and use ReqIF as the standard exchange mechanism and even do round trips. ReqIF is not the only standard to allow this generic nature in the field of Requirements Engineering. DOORS, for example, has an extensible database allowing users to add/delete attributes. The changes to the schema are often communicated to the partners by external means to replicate the changes in their database. Since ReqIF carries the meta-information with it, the changes are migrated automatically across tools/company boundaries. Transmitting the meta-information in ReqIF could however be controlled by tooling. This nevertheless would beat the purpose of ReqIF.
It is also questionable, why such a generic model is required when we have metamodels like UML or EMF already available. The reason for this is very much the same as why EMF co-exists with UML. ReqIF is not a general purpose modeling language like UML or EMF, but more focused on requirements domain.
RMF provides ReqIF as an EMF based metamodel. This could be used by tool vendors as the internal tool model or an export model by means of model to model transformation. The provided loaders and serializers make sure that the ReqIF file is read/written according to the ReqIF XML Schema.
Using ReqIF natively brings all the advantages of ReqIF to the tooling as well. For example, ReqIF based tools could model the requirements domain of the company within the tooling and share it with partners along with the instance data.
The initial code contribution is planned by early August 2011 and will be made available as soon as the IP review at Eclipse is complete. If you have any suggestions/comments about RMF, would like to contribute or like to be listed as an interested party, please provide it here.Images from FreeDigitalPhotos.net