SysML - DE Ontology Handbook 2.0 v46

Table of Contents

Introduction
Overview
Position in Knowledge Hierarchy
Details
Practical applications and examples
- Catapult Case Study
Associated Diagrams

Introduction

SysML is a standardized modeling language used to design and analyze complex systems. It provides a visual way to describe system structure, behavior, requirements, and constraints, making it easier for engineers to communicate and collaborate on system design.

SysML is a key tool in Model-Based Systems Engineering (MBSE), helping teams move away from document-based systems engineering toward model-based approaches.

Overview

SysML (Systems Modeling Language) is a general-purpose modeling language for specifying, analyzing, designing, and verifying complex systems. It extends the Unified Modeling Language (UML) with additional constructs specifically tailored for systems engineering. SysML is widely used in MBSE to create descriptive models that define system structure, behavior, requirements, and constraints.

SysML v1 has been around for about 20 years, with SysML v2 nearing standardization by the Object Management Group (OMG). The language is particularly valuable for digital engineering (DE) as it enables the creation of models that can be aligned with ontologies for interoperability.

SysML is not the same as MBSE - MBSE is the broader methodology that uses modeling languages like SysML to support systems engineering activities.

The SysML language has four main pillars that support different aspects of system modeling:

Pillar

Description

Structure

Describes system components, their relationships, and interfaces

Behavior

Describes how the system operates, including sequences and states

Parametrics

Defines mathematical relationships between system parameters

Requirements

Specifies what the system must do or achieve

Position in Knowledge Hierarchy

Broader concepts: - Part II (is-a)

Narrower concepts: - BDD (is-a) - IBD (is-a) - Parametric Diagram (is-a)

Details

SysML Diagram Types

SysML supports multiple diagram types that help engineers visualize different aspects of a system. The main diagram types include:

Diagram Type

Purpose

Block Definition Diagram (BDD)

Shows structural decomposition of a system into blocks and their relationships

Internal Block Diagram (IBD)

Shows parts, interfaces, and flows within a block

Activity Diagram

Describes control and data flow of asynchronous activities

Sequence Diagram

Shows interactions among distributed objects or services via sequences of messages

State Machine Diagram

Describes sequences of states that an object or interaction goes through

Parametric Diagram

Specialized Internal Block Diagram enforcing mathematical rules across properties

Requirement Diagram

Defines requirements and their relationships

SysML in the Digital Engineering Context

In the context of digital engineering and the Armaments Interoperability and Integration Framework (IoIF), SysML serves as the foundation for creating descriptive models that can be aligned with ontologies. The IoIF framework uses SysML models to configure workflows for cross-domain analysis.

SysML models must be properly structured and tagged with ontology metadata to work effectively with IoIF. This tagging is typically done using SysML stereotypes.

The following example shows how SysML blocks and properties are used to represent a catapult system:

block Catapult {
  property launchArm : LaunchArm;
  property projectile : Projectile;
  property maxRange : Real = 4.0; // In meters
}

block LaunchArm {
  property length : Real;
  property mass : Real;
  property springConstant : Real;
}

block Projectile {
  property mass : Real;
  property diameter : Real;
}

In the Catapult example, the maxRange property is a value property that represents a mission objective. This property is used in the Assessment Flow Diagram (AFD) to calculate performance metrics.

Ontology Alignment with SysML

SysML models can be aligned with ontologies using metadata, typically through stereotypes. This alignment allows the models to be integrated with IoIF for cross-domain analysis.

The metadata must be applied consistently and unambiguously to ensure IoIF can correctly interpret the model elements.

The following example shows how a SysML block can be tagged with ontology metadata:

<<catapult>> block Catapult {
  property maxRange : Real = 4.0;
  property impactAngle : Real;
}

In this example, the [catapult] stereotype indicates that the Catapult block corresponds to a class in the Catapult ontology.

Without proper ontology alignment, IoIF cannot effectively integrate the SysML model with other domain-specific models and analyses.

Practical applications and examples

Catapult Case Study

The Catapult case study demonstrates how SysML is used in digital engineering workflows. The SysML model includes:

A Block Definition Diagram (BDD) showing the structural decomposition of the catapult system
An Internal Block Diagram (IBD) showing the internal components and interfaces
A Parametric Diagram (AFD) showing the mathematical relationships between parameters

graph LR A[Catapult System] --> B[Launch Arm] A --> C[Projectile] B --> D[Spring Constant] B --> E[Length] C --> F[Mass] D --> G[Max Range] E --> G F --> G G --> H[Impact Angle] G --> I[Flight Time] G --> J[Impact Velocity] G --> K[Range] G --> L[Circular Error Probability]