This document describes Harish Narayanan's experiences using Capella at NEXTRAIL GmbH to model railway systems. It discusses how NEXTRAIL focused on systems and data modeling using Capella. It also provides an example of how Harish modeled requirements for an Automatic Train Operation track side unit project using use cases, capabilities, functions, and exchange scenarios in Capella. The document concludes with some proposed improvements to Capella, such as better linking of classes to enumerations.

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14/10/2020
An Adventure with Capella
A study from NEXTRAIL
#CapellaDays
Harish Narayanan
NEXTRAIL GmbH
Railway Systems Engineer
@harishnarayanan

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Contents
1. Kick-off to the adventure
2. NEXTRAIL’s focus points on Capella
3. Project specific experiences/analysis with Capella
4. Possible propositions for improvised modelling in Capella

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Contents
1. Kick-off to the adventure
2.
3.
4.

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Kick-off to the adventure
Who is Harish?
 24 Years old
 Railway Engineering Graduate from Technical University of Munich (M.Sc.)
 Working as Systems Engineer at NEXTRAIL GmbH
 Area of expertise – Automatic Train Operation (ATO)
Harish Narayanan
Likes to
Cook, Eat,
Travel …

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Kick-off to the adventure - Personal Experiences with Capella
 Capella is comparatively easier to comprehend, as a first time modeller in Capella
 Capella is easy to navigate in terms of GUI
 Highly interactive in terms of viewpoints
 Especially the Representations per category option
 Layered architecture modelling approach is beneficial, in terms of separating the needs of systems
 Hierarchy of elements provided in the modelling approach for interfaces is exceptional!
 E.g. From creation of a data type to allocation of respective class in an functional exchange
Design Layers from Capella

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Contents
1.
2. NEXTRAIL’s focus points on Capella
3.
4.

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NEXTRAIL’s focus points on Capella
Two major focus points,
 Systems modelling - SysML based
 Data modelling/Object Modelling – UML based
Systems Modelling:
 Used Capella to develop model based system requirement specifications
 Using Use cases, Exchange scenarios, Functional flow diagrams, system architecture, data models (if needed), etc.
Data Modelling/Object Modelling:
 Used Capella to develop object models for interface specifications
 Using Class diagrams, Exchange scenarios, exchange items, etc.

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Contents
1.
2.
3. Project specific experiences/analysis with Capella
4.

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Project specific experiences with Capella
 Involved with development of system requirement specifications for a Automatic Train Operation – Track side unit
(ATO-TS)
 The project scope needed development of model based specifications using semi-formal model i.e. Use cases and
sequence diagrams
 Capella served as a perfect fit meeting our MBSE needs.
 Added perk was Capella being open source.
 Layer based approach proved effective to identify project specific aspects for each layer.
ATO-TS and ATO-OB interaction with
Environment
ATO-OB
Train Equipped
with ATO
Wireless
Communication
ATO-TS
ATO-OB
Train Equipped
with ATO
Wireless
Communication

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ATO-TS as a viewpoint in the ATO architecture
Simple ATO over ETCS Architecture
ATO-TS in a nutshell
It is the track side system that
manages several ATO-OB units
(Trains) with in a particular area
along with the timetable data,
infrastructure data, and status
reports between them.

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Modelling Practices - Explored aspects in Capella
 The model was designed under the system analysis (SA)
 For every Use case,
 Appropriate Capabilities were created (MCB)
 Appropriate Functional block diagrams were created (SFDB)
 Appropriate Exchange scenarios were created using the pre-defined functions (ES)
 Useful functionality from Capella which allows the functions to be used in ES’s provided a more holistic
understanding of the model
 Requirement modelling and linking

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Modelling Practices - Process definition using a Meta model
System Analysis - Meta model
A snip of Meta model

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<<elaborates>>
MCB SDFB
ES
Modelling Practices - System
requirements modelling
process workflow
 An elaborated view with an
example use case and
relations between them
 Approach based on the
meta model
Example – elaborated view point using the meta model

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Example Use case – Status Report Management
 Status report management is one of the imperative use cases of the ATO-TS
 Prime focus / Use case story:
 Forward the status reports from Trains to Traffic management systems
 Forward the train capability reports from Trains to Traffic management systems
 To generate and transmit acknowledgement reports to respective actors
 Modelling approaches:
 Designed as a generic use case
 Includes the management of multiple features i.e. status reports and train capability reports
 Additional Exchange scenarios can be defined, when/where needed
Snip of ATO-TS and ATO-OB
Interface

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Example Use case – Status
Report Management
 System data flow bank diagram of
Status report use case
 Provided better segregation of
functions with the help of System
and actor functions
 Use of Super functions for ATO-
TS functionalities
Actor function
System function Actor function
Super function
Sub-functions
SDFB – Status report management

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Example Use case – Status
Report Management
 Exchange scenario for a status
report from ATO-OB to CTMS
through ATO-TS
 Impacts of underlying SDFB’s,
 Improved visual stimulus
through the functions
 Faster ES instantiations
ES - Status report
management

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Modelling Practices – Integration with Team for Capella
 Initially the project began without Team
 Challenges were faced in terms of sharing models, combining work, creating backups, etc.
 Later, Capella integrated with Team provided us with a safer modelling environment
 Automatic model backup facilities
 Better work splits
 Remote working

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Contents
1.
2.
3.
4. Possible propositions for improvised modelling in Capella

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Possible propositions for improvised modelling in Capella
 Classes linking to ENUM lists (Data modelling)
 Providing relations from classes to ENUM lists were not possible, but linking the ENUM list through the properties was
possible
 When present, it can provide better visual paradigms to the data modelling
 Add-ons to convert Capella models to other SysML based software’s and vice-versa
 Can help to explore several new modelling aspects from other software’s
Example - Class Diagram relation

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Possible propositions for improvised modelling in Capella
 More aspects to improve the framework of a diagram e.g. options to add a frame around a use case diagram to provide
heading and subheadings
 Merge/Diff function for local models
 When it supports with transfer of representations as well in addition to model elements, it shall prove to be very
powerful function
ATO-TS UC20: Status ReportManagement System
Example – Diagram framework

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Q&A session!

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Thank you.
NEXTRAIL GmbH
Schlüterstraße 39
10629 Berlin
Schaumainkai 91
60596 Frankfurt a.M.
Harish Narayanan
T: +49 151 46760926
E: harish.narayanan@nextrail.com

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