Over the last years, numerous modelling platforms have been developed to simplify and automate many steps of Model Driven Engineering (MDE) processes. However, still several challenges have to be solved for enabling a wider adoption of MDE. One of the most important impediments in adopting MDE tools is related to the reduced flexibility of existing modelling platforms that do not permit to relax or enforce their rigidity depending on the stages of the applied development process. For instance, EMF does not permit to enter models which are not conforming to a metamodel. On one hand this allows only valid models to be defined, but on the other, it makes the corresponding pragmatics more difficult. Thus, there is an increasing need for techniques supporting flexibility in a wide range of modelling activities, including metamodel, model, and model transformation development and reuse.

In order to tackle these challenges, the FlexMDE series of workshops started in 2012 under the name of XM ("eXtreme Modelling"). XM was held for three editions, which in 2015 continued under the name of FlexMDE. All editions have been held as satellite events of the MoDELS conference. More information about the workshop series can be found at http://www.di.univaq.it/flexmde/. Along these 7 years, we have published special issues associated with the workshop on the Journal of Object Technology [2] and the Computer Languages Systems & Structures Journal (Elsevier) [1].

The primary goal of the workshop is to identify the difficulties in the current practice of MDE related to the lack of flexibility. FlexMDE encourages contributions of ideas, concepts, tools and techniques also from other areas of software development which could be useful to revise certain MDE fundamental typing concepts, and to define agile model sketching techniques.

In the 4 th edition, FlexMDE initially received 5 submissions, 4 of which materialized into papers. The committee accepted all 4 papers, and the program included an invited talk by Prof. Thomas Kühne from the Victoria University of Wellington (New Zealand).