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+HTTP interface
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+==============
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+
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+If you want to use the Modelverse on an as of yet unsupported platform, you will have to make use of the HTTP interface directly.
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+While it is possible to directly send HTTP requests, it is recommended to create a wrapper, similar to the Python wrapper mentioned before.
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+Otherwise, many of the more complex operations (e.g., process enactment) will quickly result in problems.
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+Now follows a detailed description of how the HTTP interface works.
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+An explanation of the semantics of these operations can be found in the Python wrapper.
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+An example implementation can be found in the Python wrapper, which should prove a valuable starting point for creating a new interface.
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+
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+Request and Reply format
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+------------------------
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+
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+HTTP requests to the Modelverse use the POST format, and should be directed at the location at which the Modelverse server is running.
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+The request itself is a URL encoded form of the following dictionary: {"op": operation, "value": value, "taskname": taskname}.
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+In this format, the operation is either *set_input* or *get_output*, with the logical meanings (see further).
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+Value is only present if the operation is *set_input*, and contains a JSON serialized value to set as input.
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+For multiple simultaneous requests, it is possible to not use a key *value*, but a key *data*.
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+If the data key is present, this should contain a JSON serialized representation of multiple invocations.
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+The semantics is identical, except that only a single HTTP request (and reply) is used.
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+Finally, the taskname indicates the task to which the request is targetted.
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+Tasknames are provided by the Modelverse when necessary.
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+Fetching data from the Modelverse is done using the *get_output* operation, which is blocking until an output is present.
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+Note that a timeout might occur if no output becomes available within the time specified as the HTTP output.
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+This is not a problem, but should be handled.
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+Output requests are handled in a FIFO manner, as multiple calls can be made for output simultaneously.
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+
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+Apart from the primitive types usually supported by JSON, action language primitives can also be sent.
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+These are JSON serialized as a dictionary, with a single key *value* and its value being the string representation of the element.
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+For example, an *If* construct is serialized as {"value":"If"}.
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+The Modelverse understands this special case, but your interface should also be able to handle such data.
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+Note that communication of these internal primitive types is extremely rare.
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+
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+The reply to this request is simple.
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+For a *set_input* operation, the reply merely indicates that the input is put in the input queue of the task, and the content of the reply can be ignored.
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+For a *get_output* operation, the reply contains a JSON serialized representation of the output data put in the Modelverse.
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+This is always a primitive type of JSON, and will never be a list or dictionary.
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+
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+.. note::
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+ Communication over HTTP uses a POST request to allow for unlimited amounts of data to be transfered.
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+ Instead, the request parameters, normally part of the GET URL, are sent as data of the POST request.
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+ The Modelverse ignores GET requests.
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+ This nicely follows the REST standards, as all requests indeed alter the state of the Modelverse (contrary to GET requests).
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+
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+Examples
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+^^^^^^^^
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+
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+To send the integer 1 to the task with name abc in the Modelverse, send the following data in the POST request::
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+
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+ op=set_input&value=1&taskname=abc
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+
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+To send the string def to the task with name xyz in the Modelverse, send the following data in the POST request::
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+
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+ op=set_input&value="def"&taskname=xyz
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+
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+To send both the integer 1 and the string def to the task with name abc in the Modelverse, send either two seperate requests, or a single request::
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+
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+ op=set_input&data=[1,"def"]&taskname=xyz
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+
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+To fetch the output value of a task xyz in the Modelverse, send the following HTTP request, which yields (possibly) the following answer::
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+
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+ op=get_output&taskname=xyz
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+
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+ "The output value is a string containing a JSON serialized value."
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+
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+Startup
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+-------
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+
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+When starting up the Modelverse, only a simple task manager is running.
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+To startup a new task, the task manager should be informed of the new name of the task, by sending it input.
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+This is done using the following request::
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+
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+ op=set_input&value="name_of_new_task"&taskname=task_manager
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+
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+There is no reply from the task manager, and it is assumed that the task can now be used for communication.
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+From this point on, communication with the created task can commence, following the operations specified next.
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+
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+.. warning::
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+ This behaviour is likely to change in the near future, where the task manager will output the name of a new task, thereby preventing conflicting tasknames.
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+
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+Operations
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+----------
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+
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+Upon startup of a task, the communication starts in verbose mode to allow for interactive use.
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+This means that initially, every sent input will result in one (or multiple) output values.
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+For a wrapper this is cumbersome, as it creates a lot of HTTP requests, and therefore it can be disabled with the input *quiet*.
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+A more detailed overview of all operations, their order and possible interleavings, and their possible responses, we refer to the SCCD model in *wrappers/classes/modelverse.xml*.
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+
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+The first two input values that are to be sent are the username and password, which can happen using the following request::
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+
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+ op=set_input&data=["my username","my password"]&taskname=name_of_new_task
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+
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+Depending on the output values received, it can be determined whether this is a new or existing user.
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+If this is a new user, a subsequent request should again send the password to confirm the password.
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+If this is an existing user, the task continues and is now logged in.
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+
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+When logged in, there are three possible modes: megamodelling, modelling, and service.
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+Apart from the responses mentioned here, several other responses are also possible, though these are exceptions.
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+All ordinary responses to operations start with *Success:*, or merely *Success* if there is no value to output.
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+
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+Megamodelling
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+^^^^^^^^^^^^^
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+
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+In megamodelling mode, which is the first mode to be entered after login, users can modify the megamodel, containing the relation of all models in the Modelverse.
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+It is in this mode that new models should be created, models should be deleted, or new transformations be defined.
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+Additionally, as all user access control is modelled explicitly, this is also the mode in which user management is done.
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+
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+There are two operations to allow mode switching: *model_modify* and *service_register*.
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+To go to modelling, send *model_modify*, followed by the name of the model you wish to open and the name of the metamodel that should be used.
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+For example::
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+
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+ op=set_input&data=["model_modify","formalisms/ProcessModel","formalisms/SimpleClassDiagrams"]&taskname=xyz
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+
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+To go to service mode, send *service_register*, followed by the name of the service that is to be registered.
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+For example::
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+
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+ op=set_input&data=["service_register","HUTN_compiler"]&taskname=xyz
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+
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+In megamodelling mode, the following simple operations are supported.
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+For each request, the output normally starts with a *Success*, following the actual return value as a string.
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+As all responses are strings, there is some encoding to them (e.g., split on newlines, split on colon, ...).
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+Most are trivial to deserialize when the result comes in, and therefore we refer to the SCCD model.
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+While operation and parameters are shown distinct in the table, the HTTP request merely sends them in exactly the same fashion.
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+For example::
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+
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+ op=set_input&data=["model_mode","formalisms/ProcessModel","formalisms/PM"]&taskname=xyz
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+
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+
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+Some more complex operations are mentioned below these standard operations.
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+
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+============================= ======================================
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+operation parameters
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+============================= ======================================
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+model_move model_name, new_location
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+process_signature process_name
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+transformation_between source_name, target_name
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+model_render model_name, mapper_name, rendered_name
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+model_rendered model_name, mapper_name
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+verify model_name, metamodel_name
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+model_delete model_name
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+model_list location
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+model_list_full location
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+permission_modify model_name, permissions
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+permission_owner model_name, owner
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+permission_group model_name, group
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+group_create group
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+group_delete group
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+group_owner_add group, user
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+group_owner_delete group, user
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+group_join group, user
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+group_kick group, user
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+group_list
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+admin_promote user
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+admin_demote user
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+user_password user, password
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+transformation_read_signature transformation_name
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+verbose
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+quiet
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+folder_create location
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+add_conformance model_name, metamodel_name
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+model_types model_name
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+AL_text location
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+model_add metamodel_name, model_name, code
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+============================= ======================================
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+
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+More complex operations have multiple phases, as there is a modification step involved, or a preliminary check before the next piece of data can be forwarded.
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+These operations are presented next.
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+
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+========================= ===============================================
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+operation parameters
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+========================= ===============================================
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+model_overwrite model_name, metamodel_name
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+transformation_add_MANUAL source_models\*, target_models\*, name
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+transformation_add_AL source_models\*, target_models\*, name
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+transformation_add_MT source_models\*, target_models\*, name
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+transformation_execute activity_name, source_models\*, target_models\*
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+process_execute process_name, model_bindings\*
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+========================= ===============================================
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+
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+Parameters marked with a \* are actually dictionaries, and should be sent as such.
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+Since the Modelverse has no primitive notion of dictionaries, a dictionary is expanded as a sequence of key value pairs, terminated with an empty key.
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+For example, the dictionary {"abc": "def", "ghi": "jkl"} is sent as five individual requests (or a single data request)::
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+
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+ ...&data=["abc","def","ghi","jkl",""]&...
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+
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+For the model_overwrite operation, the Modelverse will first perform some checks as to whether the overwritten model can indeed be overwritten.
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+If so, it will output the reply *Waiting for model constructors...*, after which the actual code may be sent.
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+The operations starting with transformation_add are similar, but they have two phases.
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+First, they output the name of the merged metamodel, ready to be RAMified.
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+There is then the possibility to modify this metamodel before RAMification starts, by logging in using a different task, modifying the model, and storing the changes.
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+As soon as all changes are made, any input will initiate RAMification.
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+Second, the Modelverse will query for the code that specify the transformation.
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+For manual operations, this query is not done.
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+For AL, this query expects ActionLanguage code.
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+For MT, this query expects a model conforming to the RAMified metamodel.
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+Of course, these constructors can be passed an empty model, in which case the models have to be updated later on using model_modify.
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+
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+The transformation_execute operation and process_execute are special operations, in the sense that they (potentially) spawn other tasks.
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+The output value of these operations is the name of a newly spawned task, on which execution should continue.
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+These tasks might not be identical to other tasks, in the sense that they are purely able to communicate with the currently executing operation.
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+This operation is rather complex, and we refer to the SCCD model for detailed information.
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+The process_execute operation is similar, but instead of outputting only a single taskname, we output multiple, combined with the activity that spawned it.
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+
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+Modelling
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+^^^^^^^^^
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+
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+In modelling mode, a single model is opened and ready to be modified.
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+There are several supported operations, most of which are simple to use.
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+To switch back to megamodelling mode, send the *exit* input.
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+
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+============================ =============================
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+operation parameters
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+============================ =============================
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+help
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+instantiate_node type, element
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+instantiate_edge type, element, source, target
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+attr_add element, attribute, value
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+attr_delete element, attribute
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+attr_name element, attribute, name
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+attr_type element, attribute, type
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+attr_optional element, attribute, optional
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+delete element
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+list
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+list_full
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+JSON
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+read_outgoing element, type
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+read_incoming element, type
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+read element
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+read_attrs element
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+read_defined_attrs element
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+types
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+retype element, type
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+read_association_source element
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+read_association_destination element
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+connections_between element, element
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+all_instances type
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+define_attribute element, attribute, type
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+undefine_attribute element, attribute
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+============================ =============================
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+
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+Some additional operations are again available that work in two phases.
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+These operations are *attr_add_code* and *upload*, which first perform some checks and then wait for AL code or a model.
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+
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+Service
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+^^^^^^^
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+
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+In service mode, the Modelverse blocks until the input *service_stop* is received, and this task is used to process the service.
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