See also: OATC Wiki Home
Date: July 1, 2010
Time: 09:00 - 10:30 am
Venue: Skype Conference Call
Topic: Extendable version of OpenMI 2 (continued)
Table of contents
Participants
Rob Knapen, Alterra, Wageningen UR (Rob.Knapen@wur.nl)
Standa Vanecek, DHI (s.vanecek@dhi.cz)
Adrian Harper, Wallingford Software (adrian.harper@wallingfordsoftware.com)
Stef Hummel, Deltares (stef.hummel@deltares.nl)
~don, Deltares (gennadii.donchyts@deltares.nl)
~jgr@dhigroup.com, DHI (jgr@dhigroup.com)
Peter Schade, Bundesanstalt fuer Wasserbau (peter.schade(at)baw.de)
1. Progress towards OpenMI 2 Beta release
1.1. Source code update status - C#
1.2. Documentation updates
(Peter) Suggestion: Until 9. July mainly specify the IBaseLinkableComponent and a small general explanation of the Time+Space extension. The full Time+Space specification should follow after the sdk has been updated and tested.
(Stef) Maybe keep the documentation more or less as is, and only clearly describe the 'base' - 'timespace' leveling.
To be decided 
2. Ongoing discussion topics
2.1. Note about OpenMI 2 compliancy
2.1.2. Two level compliancy
The compliancy with the OpenMI 2 standard is split into two levels. The OpenMI compliancy on the first level refers to basic interfaces whereas the OpenMI extension-compliancy includes additional interfaces, e.g. for time and space dependent components.
The IBaseLinkableComponent is the key interface in the OpenMI standard version 2.
OpenMI-compliance definition:
1. An OpenMI-compliant component must implement the IBaseLinkableComponent interface according to the specifications provided as comments in the OpenMI.Standard2 interface source code.
2. An OpenMI extension-compliant component must implement the IBaseLinkableComponent interface and at least one of the extension interfaces according to the specifications provided as comments in the OpenMI.Standard2 interface source code. *
3. An OpenMI-compliant as well as an OpenMI extension-compliant component must, when compiled, reference the OpenMI.Standard2.dll, which is released and compiled by the OpenMI Association.
4. An OpenMI-compliant as well as an OpenMI extension-compliant component must be associated with an XML file, which complies to (can be validated with) the OpenMICompliancyInfo.xsd schema. This file must be submitted to the OpenMI Association.
5. The OpenMI Association provides two additional interfaces that OpenMI-compliant components may or may not implement: the IManageState interface and the IByteStateConverter interface. However, if these interfaces are implemented, each method and property must be implemented according to the comments given in the OpenMI.Standard2 interface source code.
6. The OpenMI Association's downloadable standard zip file provides the only recognized version of source files, XML schemas and assembly files.
* at 2.: This leads to a main difference between OpenMI 1.x and OpenMI 2. In order to become 1.x compliant the classical time and space dependent component just had to implement the basic ILinkableComponent. This component would have to implement the basic and the time and space specific extension interfaces for becoming OpenMI 2 compliant.
Decision 
: We choose for the second description, including the rephasing of Jesper
2.1.3. What does the compliancy definition mean for the user?
(Peter's todo: rephrase)
"Linking OpenMI 2 compliant components has become much more flexible than it used to be with OpenMI 1.x. Components with different concepts or in OpenMI language extensions can exchange their data. A component with the classical Modified Julian Day time definition can for example provide a consumer component, defining its simulation time by an index, with data. The provider would implement the time and space extension whereas the consumer could implement an extension for index-related dictionaries. The provider should contain an AdaptedOutput converter using both time definitions and thus being able to convert the time to the index value. More knowledge about the underlying extensions is required from the user in order to select the appropriate items and to check the plausibility of the results. This is the price being paid for higher flexibility, less due to the OpenMI but to the complexity of the task.
If both LinkableComponents implement the same OpenMI extension interface, their provider consumer relationship will remain as straight forward as with OpenMI 1.x, the conversions in AdaptedOutput will be easier to use.
When writing this documentation in Summer 2010, only the base interfaces and an extension for the classical time and space dependent components are available. Future extensions could support parallel computing, compliancy with the standards of the Open Geospatial Consortium OGC and much more.
One should remember that compliancy does not mean a pure plug and play connection. From the technical point of view most of the input and output of two LinkableComponents can be connected for data exchange. But neither the standard nor the related sdk offer too much methods for checking the correctness of the selected variables. The user has the responsibility for selecting the appropriate quantities and the locations where they are defined. The approved, but updated interface definitions as well as the extensions preserve the slimness of the OpenMI."
(Adrian)
"Potential users of an OpenMI compliant component should understand the following point
"Being compliant is no guarantee that it can be usefully linked to another OpenMI compliant component. It is a necessary but not sufficient condition."
To be usable the user must also consider the following factors
1. Do both components target the same system infrastructure. Currently Java and .Net components cannot be mixed within the same composition.
2. Do both components implement the same OpenMI version. Development is under way to allow 1.4 components to be loaded alongside version 2 components within version 2 of the configuration editor; however, currently this is not possible. Even when possible, there will still be restrictions as version 2 of the standard exposes new (additional) data exchange concepts which are incompatible with version 1.4
3.Do both components provide and consume all the required data interactions for the underlying physics for the two models interaction. Breaking the underlying physics will cause instabilities (at best) or wrong answers (at worst). The underlying issue here is that OpenMI provides the means to couple models together, but cannot make judgements on the advisability of doing so. The responsibility for this lies with the user; it is expected that they should have competence in the use and application of both models.
4. Are all required output adapters implementations compatible. Version 2 allows for adapters tailored for specific applications and hence some combinations could be invalid. Whilst it can be reasonably expected that adapter implementations from the same software source (SDK) should either be compatible or create sensible runtime warnings if not (if developed well). This is unlikely to be the case when mixing adapters from different software sources. Hence, when using output adapters care should be taken to understand their implementation details."
Decision : we will move 4. to the assumptions underlying the OpenMI architecture.
2.1.4. What does the compliancy definition mean for an application developer?
todo
2.2. How to package and distribute extensions
(Rob) When an extension is approved by OATC will it be included into the Standard library (dll or jar), or will each extension be distributed in its own library?
(Peter) To keep it in the standard library will make the check on compliancy easier, s. 2.1.2. saying compliant models have to reference OpenMI2.Standard.dll/jar. One argument pro an own library is that new extensions can be more frequently updated than the standard. Anyway, I guess the OAEC has to decide formally about new extensions as it did about compliancy of models in the past.
(Jesper) I believe (at least for C#, I am not sure with java) when we first have released the OpenMI2.Standard.dll, then there are issues in case this dll is updated to include e.g. a dictionary extension: Two different OpenMI2.Standard.dll files having the same version number, but different content. It would be much more safe to release an OpenMI2.Standard.DictionaryExtension.dll, and leaving the original content in the OpenMI.Standard.dll. It may be possible to put it all in a new standard dll, however that requires "intelligent" installers: Assume I am to install a TimeSpace engine and a Dictionary engine, which come with each their version of the OpenMI2.Standard.dll that they want to install and register in the GAC. Depending on the order in which I install the engines, each installer needs to know whether they are to reregister their version of the OpenMI2.Standard.dll in the GAC, to assure that the newest version is the one registered.
2.3. Revisit discussions left out from meeting 28
There is a number of discussions there, that has not yet been decided on.
