P. Haindl, R. Plösch: Specifying Feature-Dependent Maintainability Requirements in an Operational Manner - Results From a Case Study with Practitioners, IWSM MENSURA Conference, Mexico City, Mexico, November 29-30, 2020, accepted for publication.

The TAICOS constraint language allows to express feature-dependent non-functional requirements as quantitative constraints using a compact set of time series operations, time filters, and comparison operators. For each of these  constraints, thresholds can be defined on feature-level using metrical and ordinal scales. The fulfillment of these constraints can be automatically evaluated throughout the engineering cycle and shall support data-driven decision making for improving software quality on feature-level.

In this paper we present the results of an empirical case study with 14 practitioners who formulated maintainability requirements using the TAICOS constraint language for different features in an operational manner. After formulating the constraints we asked the practitioners to rate scope, expressiveness, and suitability of the constraint language and the respective practical benefits and weaknesses of the language. Also, we condensed nine recurrent maintainability aspects from the interviews and analyzed which time series operations, filters, and data types the practitioners used for each maintainability aspect.

The case study reveals that the constraint language is expressive, suitable, and its scope fully sufficient to specify maintainability requirements on feature-level. Also, we observed that  particularly the company specific modularization of software features has an impact on the suitability of the constraint language. The practitioners positively highlighted the ease of use, compactness, and understandability of the constraint language and remarked that additional requirements engineering support is essential to effectively utilize all language capabilities.