Modeling C-based systems with UML

Modeling C-based systems with UML

November 14, 2020 | programming, c, methodologies

Introduction #

The Unified Modeling Language (UML) is used almost exclusively for Object Oriented Programming (OOP). Since embedded system design has become increasingly more complex, designers have been searching for new methodologies to manage these complexities and allowing higher productivity. Due to the exclusivity of UML for OOP, it makes it difficult for functional programmers to integrate UML concepts into the modeling because the transformation of many UML concepts to C is difficult and confusing .

The problem when integrating UML tools into modeling a embedded system happens because programmers require to two different ways of thinking: (i) OO way and (ii) functional oriented way. presents a set of mapping rules on which allows UML to be applied in modeling embedded system.

Unified Modeling Language (UML) #

There are six basic UML elements:

  1. Class Defines the state, attributes and behaviour. It can be called active or abstract. The active class means a thread class that has a defined state, behaviour, attributes and has the instances of it as objects. A class can be abstract when it is in one or more states, when operations or behavior are not completely defined, when in an abstract stage, or when it is not for creating objects but only inheritance can create the objects.
  2. Package A packed collection of classes and objects.
  3. Stereotype
  4. Object An instance of a class that is a functional entity formed by copying the states, attributes and behavior from a class.
  5. Anonymous object
  6. State A defined state, for example, rounded rectangle with state name for its identity.

A conceptual design can use the User Case Diagram (UCD), Object Model Diagram (OMD), Structure Diagram (SD), Sequence Diagram (SD), Activity Diagram and State-chart UML approaches.

  1. Use Case Diagram Shows the main functions of the system (use case) and the entities that are outside the system (actors). UCDs show how classes and objects interact with each other. UCDs allow requirements specifications for the system and the interactions between the system and external actors.
  2. Structure Diagram Helps defining the system structure and identify large-scale organizational pieces of the system. It allows flow visualization of information between system components and the interface definition through ports.
  3. Object Model Diagram Specifies the structure of the classes, objects and interfaces in the system and the static relationship that exist between them.
  4. Sequence Diagram Describes how structural elements communicate with one another over time and identifies the required relationships and messages.
  5. Activity Diagram Describes the dynamic aspects of a system and the flow of control from activity to activity, allowing visualization of interactions between the system, the environment and the interconnections of behaviors for which the subsystem or components are responsible.
  6. State-chart Defines the behavior of classifiers (actors, use case or classes), objects, including the states they may enter over their lifetime, messages, events or operations on which causes the transition from state to state.


A C-language software is a function oriented design with header files, function files, local and global variables, flow charts, state diagram and etc. Due to UML having no direct support for C-language, does not cover all the aspects of the code, but rather replaces or transforms some of the feature.

In this strategy, we provide rules for UML elements used only the adopted set of diagram types. Every use case in the UCDs can describe two C files (one .c and another .h header file) because each use case defines a behavior yielding an observable result and in order to reuse the result a use can be included by another use case [@wang2009modeling].

Sequence diagrams identify the sequence of function calls. In the case where a system object can have different states, as specified in the State Machines, it can be described using UML statecharts. The Activity Diagram in UML can represent the flowchart for a function use. Event triggers in those diagrams are implemented by triggering the timers, the user inputs, and interrupts, etc [@wang2009modeling].

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