Overarch

A data driven description of software architecture based on 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.

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

Features

• models and views as data
  • C4 model elements and views
  • hierarchical models
  • separation of models and views
  • extensible format
  • view specific customization of model elements
• exports
  • JSON if you need to process models with languages without EDN support
  • PlantUML/C4
    • all views (except code view)
    • styling and sprite support
  • Structurizr experimental
• watch model directory for changes

Rationale

C4 models are great to 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 but the models used for diagram generation with the existing 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.

The model data should be separated from information about these representations. They can be composed with these information 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 should be 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 should be Extensible Data Notation (EDN) with representations in other formats like JSON. EDN is a textual format for data, which is human readable. It is directly readable into data structures in clojure code.

The data format should be open for extension. E.g. it should cope with additional attributes or element types in the data structures.

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

Model references should be used to refer to model elements from representations (e.g. diagrams). To allow references to relations, the definition of a relation must have 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)

Examples

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
!include https://raw.githubusercontent.com/plantuml-stdlib/C4-PlantUML/master/C4_Context.puml

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")

SHOW_LEGEND()
@enduml

System Context View rendered with PlantUML

Container View rendered with PlantUML

Build

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

Installation

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.

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

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 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.

Usage

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]

Overarch currently supports these options

Options:

  Option                       Default   Description

  -m, --model-dir DIRNAME      models    Model directory
  -e, --export-dir DIRNAME     export    Export directory
  -w, --watch                            Watch model dir for changes and trigger export
  -f, --format FORMAT          plantuml  Export format (json, plantuml, structurizr)
      --model-info                       Returns infos for the loaded model
      --plantuml-list-sprites            Lists the loaded PlantUML sprites
      --debug                            Print debug messages
  -h, --help                             Print help

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.

Documentation

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

See Design for information about the design of Overarch.

Copyright

© 2023 Ludger Solbach

License

Eclipse Public License 1.0 (EPL1.0)