Both, the data and the communication of the METK are controlled by the METKManager. The core of the METKManager is an http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr. The http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr is a concept of http://www.mevislab.de/MeVisLab to hold data in three staged hierarchy (objectID, layerID, infoID). These data can be read and written by other modules, connected to the http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr. Changes of single values are communicated to all connected modules. Each module can listen to several entries and so react on changes. For more information read the documentation of the http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr.
To get the data and to communicate with other METK modules each METK module needs to be connected to the METKManager. It can be connected directly or via other METK modules' METK output, which leads to a better network design. The METKManager loads a case and stores all information about the segmented structures, case information and communication values in its http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr. All METK modules can access and manipulate these data. So, if one module change the color of a structure, are other METK modules can react on this event and can where required adjust their own settings.
Some data, like the Communication object are only for communication. Those values are not stored in the cases and are only hold to send events and messages to other METK modules.
The core of each METK module to connect itself with the METKManager (better: the internal http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr) is an ObjInfo module (please see also the http://www.mevislab.de/fileadmin/docs/MLabModules/std/help/html/private/ObjMgrFrame.htmlObjMgr documentation for information about this module).
For more information on the data structure see File format.