===== Introduction to Capella : features and capabilities ====
By Hguen Hyu (dyknguen@edu.hse.ru)

==== Keywords ====
Capella, Modeling tool, ARCADIA, Capella’s features, Capella’s capabilities, MBSE, System Engineering, Model.

==== Abstract ====

In addition to being a standard modeling tool, Capella is an engineering based modeling tool that proves to be useful in different industries. Capella which is based on a graphic interface integrates architectural design practices in system as well as software engineering and hardware design philosophies based on a model oriented approach termed.

The ARCADIA/Capella Domain-Specific Modeling Language consists of UML/SysML and NAF influenced languages, having a lot of cross-language architecture concepts. This language was developed through several rounds of definition by systems and software architects from multiple domains, including transportation, aviation, space, and radar. This method introduces a structured engineering process that incorporates different phases focusing on the analysis of customers’ needs and the analysis of the solution space and systems architecture. My case is quite different, however; in the next chapter, I plan to focus on the summarized features of Capella and show where its strengths lie.

==== Introduction ====

The origins of Capella stem from Thales Group's internal need for a powerful MBSE tool [1]. Initially developed as a proprietary solution, it was later released as an open-source project under the auspices of the Eclipse Foundation. This transition marked a significant milestone in democratizing access to professional-grade systems engineering tools.
More than a conventional modeling tool, Capella is a model-based engineering solution successfully deployed in various industrial contexts. Built on a graphical modeling platform, Capella provides systems, software, and hardware architects with rich methodological guidance, based on ARCADIA - a comprehensive model-based engineering approach that :

** - **  Ensures thorough collaboration in engineering by sharing a common reference architecture
 
** - **  Manages system and architecture complexity 

** - **  Identifies the optimal architecture through trade-off analysis

** - **  Oversees various engineering levels and traceability with automated information transfer and refinement

Rooted in MBSE’s three foundational pillars, ARCADIA can be said to offer both a modeling language and a modeling methodology, both of which Capella fully understands and implements. 

{{ :arch:2024:intro_to_capella_1.png?nolink&600 |}}

Figure 1: The three pillars of MBSE with ARCADIA/Capella [4].

==== The ARCADIA ====

Arcadia stands for ARChitecture Analysis and Design Integrated Approach [3]. It is a model-based engineering methodology for designing system, hardware, and software architectures, supported by the Capella modeling tool. This methodology was developed by Thales from 2005 to 2010 through an iterative process, with input from operational architects across all Thales business sectors (such as transportation, aerospace, space, radar, and more).

This methodology provides a detailed rationale to [3] :

**-**  Understand the customer’s true needs

**-**  Define and share the product architecture among all engineering stakeholders

**-**  Verify and validate the design from the outset and justify it

**-**  Manage and streamline the Integration, Verification, Validation, and Quality (IVVQ) process

Arcadia can be applied to complex systems, devices, or the definition of software or hardware architectures, particularly in cases involving stringent constraints that must be reconciled (e.g., cost, performance, safety, security, reusability, consumption, weight).

The approach emphasizes a structured process through successive engineering phases, helping to clearly separate needs (operational needs analysis and system needs analysis) from solutions (logical and physical architectures).

{{ :arch:2024:intro_to_capella_2.png?nolink&600 |}}


Figure 2: ARCADIA engineering levels [2]

**Customer Operational Need Analysis** - Tasks : Define operational capabilities , perform an  operational need analysis.

**System/SW/HW Need Analysis** - Tasks : Perform a capability trade-off analysis ,  perform a functional and non-functional analysis, Formalise and consolidate requirements.

**Logical Architecture design** - Tasks : Define architectural drivers and viewpoints, Build candidate architectural breakdowns in components, Select best compromise architecture.

**Physical Architecture design** - Tasks : Define architectural patterns , Consider reuse  of existing assets design a physical, Design a physical reference architecture, Validate and check it.

** Development Contracts** - Tasks: Define a components IVVQ strategy, Define and enforce a Pbs and component integration contract.

==== The Capella Modeling Tool ====

Capella -  Open Source MBSE solution to specify and design products architecture To successfully specify and design new products, systems architects need a tool to better communicate, analyze and reuse components and architectures. They also need a system engineering method to guide them through the process of identifying needs and specifying the solution that meets the customers requirements and realizes the expected functions [5]. 

**Methodological Guidance**

The Capella workbench, built on the Eclipse platform, implements the ARCADIA method, offering a Domain Specific Modeling Language (DSML) and a tailored set of tools. One notable feature of Capella is its built-in methodology browser, which reinforces ARCADIA's principles while providing clear, effective guidance for users. This activity browser organizes key Capella activities methodologically, guiding users through creating essential diagrams step-by-step. Serving as the primary access point for model creation, it is designed to support both newcomers and experienced users alike.

**Semantic Colormap**

Since graphical representations are essential for effective communication, Capella uses a unified color scheme: elements related to functional analysis are shown in green, while components engineering appear in blue ,  Data models and interfaces are shown in pink  . This approach significantly improves model readability for all stakeholders, including architects, V&V experts, specialty engineers, and managers. Another valuable feature of Capella is its contextual semantic browser, which enables navigation of model elements outside of the diagrams. More intuitive than the typical hierarchical view, the semantic browser quickly provides relevant contexts for elements through targeted queries, making it the preferred tool for exploring models, diagrams, and analyzing relationships between elements.

**Semantic Browser**

The semantic browser is more practical than the standard hierarchical model view, instantly offering context for model elements through relevant queries. It serves as the preferred tool for navigating models and diagrams, allowing for quick analysis of relationships between elements.

**Computed Links**

A notable feature of Capella is its scalability and its capacity to handle growing model complexity. Capella automatically performs graphical simplifications, displaying information exchanges from lower-level functions at higher functional levels. This helps architects by eliminating the need to manage intermediate exchanges manually and maintain consistency across various abstraction levels. Additionally, Capella offers a tag-based system to visually group exchanges that are semantically related.

**Advanced Diagram Management**

Automated contextual diagrams in Capella allow content to be updated automatically based on selected elements and preset semantic rules. The synchronization/unsynchronization feature provides detailed control over which elements are consistently shown or hidden, such as function ports, component exchanges, and class properties. Filters enhance diagram readability by enabling selective display options that automatically show or hide specific elements. Additionally, layers offer customization of diagram visuals according to different perspectives or specialty viewpoints.

**Model Validation**

Capella categorizes model validation rules into areas such as integrity, design, completeness, and traceability. Architects can create validation profiles tailored to specific aspects of the model. When applicable, quick fixes offer automated solutions for rapid problem resolution.

**Semantic delete with preview**

Capella provides instant impact analysis of deletions.

**Replicable elements and libraries**

Replicable Elements serve as mechanisms that facilitate the easy reuse of model components, potentially across multiple roots. A Replicable Elements Collection (REC, short for Record) defines a specific element or set of elements that can be utilized in various contexts, configurations, or models. A Replica (RPL, short for Replay) represents an instance of a REC. These RECs can be organized into libraries that are shareable across multiple projects.

**Transition System/Subsystems**

The automated and iterative transition between systems and subsystems significantly aids in managing multiple engineering levels. Contracts and models for the subsystems are derived from the system itself. Ideally, stakeholders of the subsystems participate in co-engineering activities at the system level prior to the transition taking place.

**Multi-Viewpoint**

Capella offers fundamental demonstration viewpoints, including Mass, Cost, and Latency. When used in conjunction with Kitalpha, it also features an API for developing custom viewpoints and a collaborative comparison view that assesses the performance of candidate architectures based on various concerns.

**HTML output**

Sharing models with all stakeholders is crucial in model-based systems engineering. By publishing and distributing HTML versions of models, these models can serve as the definitive reference for all engineering activities.

In addition, Capella provides various types of diagrams:

**Operational Architecture**: Operational architecture diagrams play a vital role in Operational Analysis by illustrating how Operational Activities are assigned to Operational Entities. Additionally, Operational Processes can be represented as prominent pathways within these diagrams.

**Capabilities**: Capabilities diagrams are present throughout all Arcadia engineering phases, with particular relevance in Operational Analysis and System Needs Analysis. Similar to UML use cases, capabilities are depicted using Dataflows, Functional Chains, and Sequence Diagrams

**Dataflows**: Dataflow diagrams are available in all Arcadia engineering levels. They represent information dependency between functions. These diagrams provide rich mechanisms to manage complexity: Computed simplified links between high-level Functions, categorization of Exchanges, etc. Functional Chains can be displayed as highlighted paths.

**Architecture**: Architecture diagrams are utilized across all phases of Arcadia engineering. Their primary purpose is to illustrate how Functions are allocated to Components. Functional Chains can be represented as prominent pathways within these diagrams. In the System Needs Analysis phase, these diagrams feature a single box representing the System being studied, along with the associated Actors. In Logical Architecture, these diagrams show the building blocks of the system. These are called Logical Components. In Physical Architecture, these diagrams also show the allocation of Behavioural Components onto Implementation Components (typically material, but not necessarily).

**Trees**: Tree diagrams depict the hierarchical breakdown of Functions or Components. Each node within the diagram can be expanded or collapsed as needed.

**Sequence Diagrams** : Capella offers various types of sequence diagrams, including Functional Scenarios, where lifelines represent Functions; Exchange Scenarios, which feature Components or Actors as lifelines and depict Functional or Component Exchanges as sequence messages; and Interface Scenarios, where Components or Actors serve as lifelines with Interface Operations represented as sequence messages. Additionally, these diagrams can illustrate Modes, States, and Functions.

**Modes and States**: Modes and States diagrams are state machines inspired by UML. They can associate Modes, States, and Transitions with Functions, Functional Exchanges, Interface Operations, and other elements.

**Classes and Interfaces**:  Capella offers sophisticated tools for modeling bit-precise data structures and establishing connections to Functional Exchanges, Component or Function Ports, Interfaces, and other elements.


==== Conclusion ====

In conclusion, Capella emerges as a powerful tool in model-based systems engineering, offering a range of features that enhance usability, collaboration, and efficiency. Its ability to handle complex models through automated processes, contextual diagrams, and scalable architecture allows stakeholders to maintain clarity and coherence across various levels of abstraction. With functionalities such as replicable elements, customizable validation profiles, and effective sharing mechanisms, Capella not only streamlines the engineering process but also fosters collaboration among all parties involved. Ultimately, these capabilities position Capella as an invaluable resource for organizations seeking to optimize their engineering practices and achieve successful project outcomes.


==== References ====
  - Wikipedia: Capella (engineering). Link: https://en.wikipedia.org/wiki/Capella_(engineering)
  - Capella Short Demo. Link: https://www.youtube.com/watch?v=v5SxNNwcnGA
  - ARCADIA method. Link: https://mbse-capella.org/arcadia.html
  - Introduction to MBSE with Arcadia and Capella. Link: https://www.youtube.com/watch?app=desktop&v=Na0izOzHhKc
  - Features and Benefits Capella. Link: https://mbse-capella.org/features.html