Chor Pe Mor Movie
Analisa Wack
Organized by the German Choral Association, chor.com is a gathering place for choir directors, singers, church musicians, music teachers, lecturers, professors and composers. Moreover, it is a location for publishers, artist agencies, concert organizers, music journalists, choir trip agencies or touring agencies to present their services and products.
Conductors of all genres and levels can participate in advanced training courses, vocal ensembles can seek new members and audiences, gather experience and make new contacts, and music publishers have an opportunity to present their latest editions and get to meet and discuss with composers.
Among the seminar speakers and choirs this time are for example Anne Kohler, Lone Larsen, Howard Arman, Ludwig Bhme, Oliver Gies, Frieder Bernius, Jim Daus Hjerne, Mara Guinand, Voces8, the Swedish vocal ensemble VoNo, Windsbacher Knabenchor, Jazzchor Freiburg, Vivid Voices, Mdchenchor Hannover, ffortissibros and Voktett Hannover.
The chor.com trade fair presents an excellent opportunity to establish contacts with publishers, producers, composers, arrangers, professors, lecturers, choir directors, choir managers, and other professionals in the field. Visitors have the opportunity to gain an overview of early music and modern choral literature, prestigious and innovative concert recordings, further education and training, technical equipment of all kinds, as well as management guidance and leisure opportunities for choirs. Entry to the trade fair is free.
The chor.com programme consists of about 150 workshops, masterclasses and reading sessions for choir directors, church musicians, teachers, lecturers, academics, composers, publishers, journalists, singers and other professionals and experts in the world of choir music. Several well-known artists and lecturers have already confirmed their participation in the 2024 chor.com.
chor.com offers its participants and visitors an exciting choral music festival with several first class concerts. These performances will feature material developed in the workshops and in addition, the chor.com concerts will provide visitors with a cross section of current trends in the German and international vocal music world.
Putting somewhat existential questions aside, what we just described is a prime example for a so-called choreography in Business Process Management. Different participants (you, the pizza place and the delivery driver) communicate in a certain choreographed fashion to achieve a common goal: In this case to sell a pizza for the monetary benefit of the pizza place and driver, and the culinary benefit of yourself. The communication is usually limited to simple message and information exchanges only, and no participant cares too much about the private actions or ponderings of the others as long as the goal is eventually reached. chor-js was made to let you model such choreographies.
In Part I of this article, we will introduce you to some features of BPMN choreography diagrams, and how we crafted chor-js to let you model them in a nice and intuitive fashion. In Part II we then dive deeper into several challenges which we faced while developing chor-js, both from a conceptual (What does the standard actually say?) as well as from a technological perspective (How do we even begin to implement this?).
Oh, and if you want to know why chor-js was presented in a nice hotel lobby in sunny Salvador, Brazil, (see the photograph above) be sure to read to the end. There we wrap up our development journey, talk about the scientific impact of chor-js, and what our plans for the future are.
The level of abstraction that can be achieved is significant: A process modeler does not need to worry about the exact internal behavior of each participant, exception paths, or other low-level features of BPMN. Instead, a choreography diagram constitutes a kind of contract specification, in which the obligations of each participant are modeled without disclosing internal information.
While chor-js inherits and adapts most of its editor tools directly from bpmn-js, choreography diagrams have some very distinct features that required us to build new ways of interacting with them. Most of these features concern the handling of participant bands, like moving them up or down and adding or removing messages.
One choreography model file can hold multiple diagrams and you can easily create and switch between them in a menu bar at the top of the editor. This is used for one of the more advanced features of choreography diagrams: call choreographies. Reusable choreography snippets can then be linked from other diagrams, similar to how call activities are used in process diagrams.
By far the biggest issue we have encountered throughout development concerns one seemingly innocuous specialty of choreography diagrams that requires us to look at the so-called BPMN diagram interchange (DI). The DI is a separate layer in the BPMN metamodel and contains purely visual presentation information such as the position of activities, the waypoints of sequence flows and more fun stuff like colors. Below is a very small BPMN model showing how the resulting XML may look like:
For some features we planned, extending existing logic was not enough and we had to create custom features. Especially handling participant bands and messages calls for novel tools and interactions. In the screenshot below you see can see some of the results as they appear in chor-js: The context menu of participant bands yields tools to move the band up (and down again), make the band the initiating one, hide and unhide the attached message and swap and create the attached participant. On a side note, we also created custom icons in the style of bpmn-js for all our additions.
Unfortunately, we do not have the space to talk about each and every extension and feature we implemented, but if you browse through the repository you will certainly find some interesting techniques and insights, which may even help you with your own projects.
While exploring the BPMN standard on a level detailed enough to implement chor-js, we often ran into minor and, sometimes, major roadblocks. Such obstacles are to be expected in a standard as large and complex, and often they disappeared on their own after some meditation. This was not always the case, however.
Not all issues could be fixed by just correcting a typo, though. Some things seem to have slipped under the radar entirely when the BPMN metamodel was conceived. One of them concerns boundary events. While the standard goes into much length as to which boundary events are allowed in choreography diagrams, one thing is missing: a way to connect said events in a model. The figure below shows a tiny excerpt from the BPMN metamodel.
This view makes it rather obvious: An instance of bpmn:BoundaryEvent can only be attached to a bpmn:Activity. But a bpmn:ChoreographyActivity is specified entirely separately, and can not be used interchangeably in this context. As a result, it is not possible to create a valid BPMN choreography model with boundary events attached to any choreography activity, despite the standard text intending otherwise.
Coming back to the picture at the beginning of this article, there obviously is a rather mundane explanation as to why chor-js was featured in that Brazilian hotel lobby. And that is due to the fact that it has had a much larger impact in the scientific community than we expected. Not long after chor-js was published, people began using it for their own research prototypes. Thus, we in turn wrote a demonstration paper describing chor-js and how it can be used, which was published and presented at the International Conference on Conceptual Modeling (ER) in Salvador, Brazil, in late 2019.
In general, we are excited every time we spot a research paper which utilizes chor-js somehow, when an issue is submitted, or when we gain a star on GitHub. chor-js was and continues to be a very interesting project for us to work on. We learned a great deal about the essentials of open-source software development, project setup and maintenance, and behind-the-scenes infrastructures.
At this point, the core functionality is all there: chor-js lets you use (almost) the entirety of the BPMN choreography diagram standard in your projects. It is easy to set up, and essentially provides the same interfaces as bpmn-js. Check out the repository on GitHub, and if you spot something to do, we are always happy about new contributors!
Jan Ladleif is a research assistant and doctoral student at the Business Process Technology chair at Hasso Plattner Institute, University of Potsdam. He is working on his dissertation about modeling and enforcing smart contracts by connecting business process management and blockchain technology. Get in touch at [email protected]
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