## 9 Conclusions  
In this paper, we presented RT-Sequencer, a successor of a DSML Sequencer [24]. The development has been driven by the inclusion of new problem domain RTC systems combined with the original problem domain, data acquisition. RT-Sequencer differentiates two types of end-users: domain experts and advanced end-users. Considering these two facts, we decided on some requirements for the RT-Sequencer. For domain experts, these requirements are:  
* Modeling remains in the hands of domain experts,
* New visual blocks to support the modeling of RTC systems,
* No GPL programming knowledge is needed to create procedures with the RT-Sequencer,
* Models for the same measurement sequence are equivalent in Sequencer and the new language RT-Sequencer,
* The complexity of the models must be kept at the same level as in the previous language Sequencer, and
* productivity using RT-Sequencer needs to be improved compared to PLC programming. For advanced end-users, we defined the following requirements for the RT-Sequencer:
* Flexible language that can define new constructs,
* Extends the DSML language with a new GPL construct,
* The ability to optimize the performance of some part of the sequences, and
* The ability to define language constructs that support single or both problem domains. The DSML RT-Sequencer is implemented within the software package DEWESoft. Before, end-users of this software package could use only the predefined Sequencer's visual blocks. In this paper, we present a new DSML where advanced end-users can define new constructs of a language. The meaning of those new constructs of a DSML is defined with C++ code, which is used further to define the modeling environment and measurement procedure definition of the RTC system. In this manner, our DSML can be observed as multi-level modeling with two different end-user roles. With this architecture, the metamodel of RT-Dewesoft can stay the same, no matter what new functionalities we need for the RTC system. However, as one limitation, we can outline that advanced end-users are limited to the API predefined for extending a modeling language, which is a potential point for future extensions. Similar to other software solutions, DSMLs evolve. Usually, after their first use, new ideas emerge, such as language constructs, further implications of usage, application domains, corrections of the development process, etc. In the study [30], it is reported that the DSL end-of-life is usually, among other reasons, due to changes in the domain that were not addressed promptly, better tooling desired by end-users, etc. Finally, this can result in the adaption of another solution. It is crucial to evolve the DSML [30] to prevent such a scenario. We confirm that extensions are one of the key factors to the success story of our DSML. As shown in paper [27], several extensions provided domain experts with new language features and tooling, even with supporting another domain. Experiences with the evolution of our DSML are one of the implications of this work for DSML researchers and practitioners from industry. Other benefits for the DSML community are specific decisions and implementation details that we have made during the development of RT-Sequencer. RT-Sequencer is still a new language. We cannot report how much assistance the customers will need from Dewesoft's language engineers to prepare sequences for RTC systems. Neither do we have information on whether customers have problems differentiating end-users roles inside RT-Sequencer. The cost of RT-Sequencer maintenance and support inside DEWESoft is yet to be observed. Besides, as one of the future directions, we foresee the evolution of models [48] on an advanced end-users level, and how this affects already defined models by domain experts. Semi or fully-automated co-evolution tools are yet to be prepared to support these transformations. Conceptualization, T.K. ([PERSON]) and T.K. ([PERSON]); methodology, T.K. ([PERSON]), M.M. and T.K. ([PERSON]); software, T.K. ([PERSON]); validation, T.K. ([PERSON]), M.M.