Don S. Batory

Feature models, grammars, and propositional formulas

Feature models are used to specify members of a product-line. Despite years of progress, contemporary tools often provide limited support for feature constraints and offer little or no support for debugging feature models. We integrate prior results to connect feature models, grammars, and propositional formulas. This connection allows arbitrary propositional constraints to be defined among features and enables off-the-shelf satisfiability solvers to debug feature models. We also show how our ideas can generalize recent results on the staged configuration of feature models.

The design and implementation of hierarchical software systems with reusable components

We present a domain-independent model of hierarchical software system design and construction that is based on interchangeable software components and large-scale reuse. The model unifies the conceptualizations of two independent projects, Genesis and Avoca, that are successful examples of software component/building-block technologies and domain modeling. Building-block technologies exploit large-scale reuse, rely on open architecture software, and elevate the granularity of programming to the subsystem level. Domain modeling formalizes the similarities and differences among systems of a domain. We believe our model is a blueprint for achieving software component technologies in many domains.

Implementing Layered Designs with Mixin Layers

Mixin layers are a technique for implementing layered object-oriented designs (e.g., collaboration-based designs). Mixin layers are similar to abstract subclasses (mixin classes) but scaled to a multiple-class granularity. We describe mixin layers from a programming language viewpoint, discuss checking the consistency of a mixin layer composition, and analyze the language support issues involved.

Reasoning about edits to feature models

Features express the variabilities and commonalities among programs in a software product line (SPL). A feature model defines the valid combinations of features, where each combination corresponds to a program in an SPL. SPLs and their feature models evolve over time. We classify the evolution of a feature model via modifications as refactorings, specializations, generalizations, or arbitrary edits. We present an algorithm to reason about feature model edits to help designers determine how the program membership of an SPL has changed. Our algorithm takes two feature models as input (before and after edit versions), where the set of features in both models are not necessarily the same, and it automatically computes the change classification. Our algorithm is able to give examples of added or deleted products and efficiently classifies edits to even large models that have thousands of features.

Modeling concepts for VLSI CAD objects

VLSI CAD applications deal with design objects that have an interface description and an implementation description. Versions of design objects have a common interface but differ in their implementations. A molecular object is a modeling construct which enables a database entity to be represented by two sets of heterogeneous records, one set describes the objects interface and the other describes its implementation. Thus a reasonable starting point for modeling design objects is to begin with the concept of molecular objects. In this paper, we identify modeling concepts that are fundamental to capturing the semantics of VLSI CAD design objects and versions in terms of molecular objects. A provisional set of user operations on design objects, consistent with these modeling concepts, is also defined. The modeling framework that we present has been found useful for investigating physical storage techniques and change notification problems in version control.

Scaling step-wise refinement

Step-wise refinement is a powerful paradigm for developing a complex program from a simple program by adding features incrementally. We present the AHEAD (Algebraic Hierarchical Equations for Application Design) model that shows how step-wise refinement scales to synthesize multiple programs and multiple non-code representations. AHEAD shows that software can have an elegant, hierarchical mathematical structure that is expressible as nested sets of equations. We review a tool set that supports AHEAD. As a demonstration of its viability, we have bootstrapped AHEAD tools solely from equational specifications, generating Java and non-Java artifacts automatically, a task that was accomplished only by ad hoc means previously.

Evolving object-oriented designs with refactorings

Refactorings are behavior-preserving program transformations that automate design evolution in object-oriented applications. Three kinds of design evolution are: schema transformations, design pattern microarchitectures, and the hot-spot-driven-approach. This research shows that all three are automatable with refactorings. A comprehensive list of refactorings for design evolution is provided and an analysis of supported schema transformations, design patterns, and hot-spot meta patterns is presented. Further, we evaluate whether refactoring technology can be transferred to the mainstream by restructuring non-trivial C++ applications. The applications that we examine were evolved manually by software engineers. We show that an equivalent evolution could be reproduced significantly faster and cheaper by applying a handful of general-purpose refactorings. In one application, over 14K lines of code were transformed automatically that otherwise would have been coded by hand. Our experiments identify benefits, limitations, and topics of further research related to the transfer of refactoring technology to a production environment.

Safe composition of product lines

Programs of a software product line can be synthesized by composing modules that implement features. Besides high-level domain constraints that govern the compatibility of features, there are also low-level implementation constraints: a feature module can reference elements that are defined in other feature modules. Safe composition is the guarantee that all programs in a product line are type safe: i.e., absent of references to undefined elements (such as classes, methods, and variables). We show how safe composition properties can be verified for AHEAD product lines using feature models and SAT solvers.

Feature oriented refactoring of legacy applications

Feature oriented refactoring (FOR) is the process of decomposinga program into features, where a feature is an increment in programfunctionality. We develop a theory of FOR that relates code refac-toring to algebraic factoring. Our theory explains relationshipsbetween features and their implementing modules, and why fea-tures in different programs of a product-line can have differentimplementations. We describe a tool and refactoring methodologybased on our theory, and present a validating case study.

Feature-Oriented Software Product Lines

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