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overarch - Image © 2019 Ludger Solbach


A data driven description of software architecture based on UML and the C4 model.

Describe your model as data and specify/generate representations (e.g. diagrams) for your model. All core and supplementary C4 diagrams except code diagrams are supported. Also UML use case, state machine and class diagrams are supported.

Overarch is not so much about how to model your architecture (see C4 Model for that), but about making these models composable and reusable.

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  • models and views as data
    • C4 architecture and deployment models and views
    • UML use case, state machine and class models and views
    • Concept models, concept maps and glossaries
    • separation of models and views
    • hierarchical models and element references
    • view specific customization of model elements
    • extensible format
  • model queries
    • criteria based selection of model elements
  • template based artifact generation for e.g.
    • project templates
    • code scaffolding
    • CI/CD pipelines
    • reports
    • custom vizualizations
  • view rendering
    • PlantUML
      • all C4 views (except code view)
      • use case, state machine and class diagrams
      • styling and sprite support
    • GraphViz
      • Concept maps
    • Markdown
      • Glossary, textual representations of graphical views
  • model exports
    • JSON if you need to process models with languages without EDN support
    • Structurizr experimental
  • watch model directories for changes


UML and C4 models are great to model and vizualize an architecture on different levels of detail with the various diagrams types. The value lies in an expressive description and visualization of an architecture with different views.

But the models used for diagram generation with the existing diagram tools are not models in the sense of generality. Especially if you describe your model in PlantUML files, these descriptions are mere textfiles.

The textfiles don't compose and you can't do anything else with these descriptions other than render them with PlantUML. The parsing process is opaque and you don't have access to the data of the model. Also the model is complected with the diagrams, as layout and rendering information is part of the model description and vice versa. The model should capture the essence of the architecture and not its representation.

If the model is described as plain data in an open format, it can be transformed into a graphical representation, e.g. into PlantUML textfiles, via the specification of views on the model.

In Overarch the model data is separated from information about these representations. Models can be composed with these views and with other models. By doing so, the model may also be used in other ways, e.g. the generation of documentation, code or infrastructure.

Even if the model is specified as data, the format is a text file (EDN, JSON) to be easily edited with text editors by the whole team and to be committed to version control, instead of being in some propriatory binary format.

The native format is the Extensible Data Notation (EDN) with representations in other formats like JSON. EDN is a textual format for data, which is human readable. It is also directly readable into data structures in clojure or java code. The data format is also open for extension. E.g. it copes with additional attributes or element types in the data structures.

The model describes the architecture (the structure) of your system(s). The elements are based on UML and the C4 model and are a hierarchical composition of the elements of the architecture.

Model references are used to refer to model elements from other models and representations (e.g. diagrams). To allow references to elements and relations, they must be given an id. Model references may be enhanced with additional attributes that are specific to the usage context (e.g. a style attribute in the context of a diagram)


This is an example of the specification of a model and some diagrams based on the Internet Banking System example of Simon Brown at C4 Model.

The complete model and diagram specifications can be found under models/banking.

Further information about modelling with Overarch can be found in Usage.

Example of a model definition

#{; actors
  {:el :person
  :id :banking/personal-customer
  :name "Personal Banking Customer"
  :desc "A customer of the bank, with personal banking accounts."}
 ; system under design
 {:el :system
  :id :banking/internet-banking-system
  :name "Internet Banking System"
  :desc "Allows customers to view information about their bank accounts and make payments."
  :ct #{{:el :container
         :id :banking/web-app
         :name "Web Application"
         :desc "Deliveres the static content and the internet banking single page application."
         :tech "Clojure and Luminus"}
        {:el :container
         :id :banking/single-page-app
         :name "Single-Page Application"
         :desc "Provides all of the internet banking functionality to customers via their web browser."
         :tech "ClojureScript and Re-Frame"}
        {:el :container
         :id :banking/mobile-app
         :name "Mobile App"
         :desc "Provides a limited subset of the internet banking functionality to customers via their mobile device."
         :tech "ClojureScript and Reagent"}
        {:el :container
         :id :banking/api-application
         :name "API Application"
         :desc "Provides internet banking functionality via a JSON/HTTPS API."
         :tech "Clojure and Liberator"}
        {:el :container
         :subtype :database
         :id :banking/database
         :name "Database"
         :desc "Stores the user registration information, hashed authentication credentials, access logs, etc."
         :tech "Datomic"}}}
 ; external systems
 {:el :system
  :id :banking/mainframe-banking-system
  :external true
  :name "Mainframe Banking System"
  :desc "Stores all the core banking information about customers, accounts, transactions, etc."}
 {:el :system
  :id :banking/email-system
  :external true
  :name "E-mail System"
  :desc "The internal Microsoft Exchange email system."}

 ; Context view relations 
 {:el :rel
  :id :banking/personal-customer-uses-internet-banking-system
  :from :banking/personal-customer
  :to :banking/internet-banking-system
  :name "Views account balances and makes payments using"}
 {:el :rel
  :id :banking/internet-banking-system-uses-email-system
  :from :banking/internet-banking-system
  :to :banking/email-system
  :name "Sends e-mail using"}
 {:el :rel
  :id :banking/internet-banking-system-using-mainframe-banking-system
  :from :banking/internet-banking-system
  :to :banking/mainframe-banking-system
  :name "Gets account information from, and makes payments using"}
 {:el :rel
  :id :banking/email-system-sends-mail-to-personal-customer
  :from :banking/email-system
  :to :banking/personal-customer
  :name "Sends e-mail to"}} 

Example of a views specification

#{{:el :context-view
  :id :banking/system-context-view
  :title "System Context View of the Internet Banking System"
  :ct [; model elements
       {:ref :banking/personal-customer}
       {:ref :banking/email-system}
       {:ref :banking/mainframe-banking-system}
       {:ref :banking/internet-banking-system}
       ; relations
       {:ref :banking/personal-customer-uses-internet-banking-system :direction :down}
       {:ref :banking/internet-banking-system-uses-email-system :direction :right}
       {:ref :banking/internet-banking-system-using-mainframe-banking-system}
       {:ref :banking/email-system-sends-mail-to-personal-customer :direction :up}]}

 {:el :container-view
  :id :banking/container-view
  :title "Container View of the Internet Banking System"
  :ct [; model elements
       {:ref :banking/personal-customer}
       {:ref :banking/internet-banking-system}
       {:ref :banking/email-system}
       {:ref :banking/mainframe-banking-system}

       ; relations
       {:ref :banking/email-system-sends-mail-to-personal-customer :direction :up}
       {:ref :banking/personal-customer-uses-web-app}
       {:ref :banking/personal-customer-uses-single-page-app}
       {:ref :banking/personal-customer-uses-mobile-app}

       {:ref :banking/web-app-deliveres-single-page-app :direction :right}
       {:ref :banking/single-page-app-calls-api-application}
       {:ref :banking/mobile-app-calls-api-application}
       {:ref :banking/api-application-uses-database :direction :left}
       {:ref :banking/api-application-uses-email-system :direction :right}
       {:ref :banking/api-application-uses-mainframe-banking-system}

PlantUML export of the System Context View

@startuml banking_systemContextView

title System Context View of the Internet Banking System

Person(banking_personalCustomer, "Personal Banking Customer", $descr="A customer of the bank, with personal banking accounts.")
System_Ext(banking_emailSystem, "E-mail System", $descr="The internal Microsoft Exchange email system.")
System_Ext(banking_mainframeBankingSystem, "Mainframe Banking System", $descr="Stores all the core banking information about customers, accounts, transactions, etc.")
System(banking_internetBankingSystem, "Internet Banking System", $descr="Allows customers to view information about their bank accounts and make payments.")

Rel_Down(banking_personalCustomer, banking_internetBankingSystem, "Views account balances and makes payments using")
Rel_Right(banking_internetBankingSystem, banking_emailSystem, "Sends e-mail using")
Rel(banking_internetBankingSystem, banking_mainframeBankingSystem, "Gets account information from, and makes payments using")
Rel_Up(banking_emailSystem, banking_personalCustomer, "Sends e-mail to")


System Context View rendered with PlantUML

System Context View rendered with PlantUML

Container View rendered with PlantUML

Container View rendered with PlantUML


Overarch is written in Clojure and gets built with leiningen. To build it, you need to have Java 11 or higher and leiningen installed.

In the cloned overarch repository, run

lein uberjar

to build a JAR file with all dependencies. This JAR file is created in the target folder and is named overarch.jar


Visual Studio Code

If you have a clojure environment in some editor or IDE, just use it. Maybe a PlantUML plugin exists for this environment too.

If not, try Visual Studio Code with the Calva and PlantUML extensions.

Calva Extension PlantUML Extension

With this setup you get an editor for the EDN files with code completion, syntax check and syntax highlighting.

Model editing

You also get integrated previews of the exported PlantUML diagrams and the ability to generate image files in different formats (e.g. PNG, SVG, PDF, ...) directly from within Visual Studio Code.

PlantUML preview

PlantUML also needs an installation of graphviz. Please read the installation instructions in the PlantUML extension on how to install graphviz for your operating system.

To get support for icons (PlantUML sprites) from the PlantUML standard library, a recent plantuml.jar is highly recommended. Please download it from PlantUML Releases and reference it in the PlantUML extension settings.

PlantUML Extension Settings

Homebrew on macOS

This project has been packaged in Homebrew for macOS users. Install it using

brew install overarch

This package includes an overarch convenience wrapper which handles tracking the location of the overarch.jar uberjar for you. This overarch command can be substituted for the java -jar overarch.jar references throughout this documentation.


Use a folder for all the data (e.g. models, view specifications) of a project. Add EDN files for the model and the view specifications. All the EDN files in the folder will be loaded.

Command Line Interface

Start the the Overarch CLI tool with java.

java -jar overarch.jar [options]

For example to generate all views for the models with some debug output, use

java -jar ./target/overarch.jar -r all --debug

Overarch currently supports these options

Overarch CLI
   Reads your model and view specifications and renders or exports
   into the specified formats.

   For more information see

Usage: java -jar overarch.jar [options].


  -m, --model-dir PATH              models     Models directory or path
  -r, --render-format FORMAT                   Render format (all, graphviz, markdown, plantuml)
  -R, --render-dir DIRNAME          export     Render directory
      --[no-]render-format-subdirs  true       Use subdir per render format
  -x, --export-format FORMAT                   Export format (json, structurizr)
  -X, --export-dir DIRNAME          export     Export directory
  -w, --watch                       false      Watch model dir for changes and trigger action
  -s, --select-elements CRITERIA               Select and print model elements by criteria
  -S, --select-references CRITERIA             Select model elements by criteria and print as references
      --select-views CRITERIA                  Select and print views by criteria
  -T, --template-dir DIRNAME        templates  Template directory
  -g, --generation-config FILE                 Generation configuration
  -G, --generation-dir DIRNAME      generated  Generation artifact directory
  -B, --backup-dir DIRNAME          backup     Generation backup directory
      --[no-]model-warnings         true       Returns warnings for the loaded model
      --[no-]model-info             false      Returns infos for the loaded model
      --plantuml-list-sprites       false      Lists the loaded PlantUML sprites
  -h, --help                                   Print help
      --debug                       false      Print debug messages

If you use Visual Studio Code as described above, you can start Overarch in watch mode from a terminal inside VS Code. Every time you save some changes in the EDN files, the views will be updated and previews can be rendered with the PlantUML extension.


See Usage for additional information on modelling and usage of the Overarch CLI tool.

See Design for information about the design of Overarch.


Here are my current plans to enhance overarch in the next releases.

  • provide relations between elements of the different models to model traceability information (e.g. from use cases to the containers implementing them or from domain concepts to domain model elements)


© 2023 Ludger Solbach


Eclipse Public License 1.0 (EPL1.0)

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