Formal Semantics of the CDL Language

We reverse-engineer a formal semantics of the Component Definition Language (CDL), which is part of the highly configurable, embedded operating system eCos. This work provides the basis for an analysis and comparison of the two variability-modeling languages Kconfig and CDL. The semantics given in this document are based on analyzing the CDL documentation, inspecting the source code of the toolchain as well as testing the tools on particular examples. 1 Semantics 1.1 Abstract Syntax Features, types and constraints. Let Id be a finite set of features, let Kinds be a set of domain-specific feature kinds and let Flavors be a set of types that further define a feature’s possible values. More precisely, Kinds = {package, component, option, interface} and Flavors = {none, bool, booldata, data}. Furthermore, we introduce two types of expressions allowed in CDL: Goal expressions and list expressions. Concerning the first one, we define Exp(Id) to be a set of goal expressions over Id, generated by the following grammar: e ::= id | const | e⊗ e |!e | ̃e | e⊕ e | e⊘ e | Func(e, e, ...) | e?e : e (1) Here, ⊗ ∈ {||,&&, implies, eqv, xor}, ⊕ ∈ {+,−, ∗, /,%, <<,>>, ˆ,&, |}, ⊘ ∈ {==, !=, <,>,<=, >=}, Func ∈{get data, is active, is enabled, is loaded, is substr, is xsubstr, version cmp}, id ∈ Id and const ∈ Data, whereas Data is a set of untyped data (say all character strings). The second type of expressions, so-called list expressions represent an enumeration of values or ranges, which can be computed by goal expressions. Thus, we define LExp(Id) to be a set of list expressions over goal expressions, generated by the following grammar (e ∈ Exp(Id)): l ::= (e | e to e) [ l ] (2) CDL models. Cdl is the set of all possible models in CDL. Each CDL model m ∈ Cdl is a set of nodes, so Cdl = P(Nodes), where Nodes = Id× ⌈Id⌉ × Flavors× P(Exp(Id))×P(Exp(Id))× ⌊Exp(Id)⌋ × ⌊LExp(Id)⌋ × Kinds× P(Id) (3) 1http://ecos.sourceware.org 2http://ecos.sourceware.org/docs-3.0/cdl-guide/cdl-guide.html