This documentation aims at developers that want to get more information about the underlying concepts and how to build and run BDeploy locally.

For people wanting to use BDeploy please refer to the end user documentation that is provided on our homepage https://bdeploy.io


The BHive (short: hive) provides a mechanism to store and transfer files over the network. It decouples storage of file content and hierarchical filesystem layout descriptions (trees). The mechanism is similar to how GIT stores files. File content is stored and identified by using the content’s checksum.

Merkle Hash Tree

Here some properties of BHive:

  • The BHive uses a Merkle Hash Tree to store data much like GIT does (similar technology is also used for implementing blockchains).

  • Consistency of objects can be verified by calculating the checksum of the content and comparing it with the name of the file storing that content.

  • BHive knows four different types of objects: BLOB (any file content), TREE (a list of BLOB, TREE, MREF entries), MREF (a reference to a to-be-nested MANIFEST), MANIFEST (associates some meta-data with a root TREE).

  • All known object types (except MANIFEST) are stored using the exact same mechanism (ObjectDatabase). This means verifying the consistency of whole trees is as simple as verifying consistency of individual files.

  • MANIFEST are stored in a separate ManifestDatabase, this is to allow named storage and reference to MANIFEST, since they are the top-level entry point into the BHive. Most high level operations will require Manifest.Key objects as parameters.

  • BHive has a command line tooling to allow direct manipulation of local and remote hives: io.bdeploy.bhive.cli.BHiveCli

  • BHive has a standalone server (using the above cli) which allows serving BHives without BDeploy.

  • A io.bdeploy.bhive.BHive does not expose API, use Hive.Operation defined in the io.bdeploy.bhive.op package to programmatically interact with a hive.

  • Hive.Operation can be implemented externally, to provide new functionality operating on a BHive from the outside.

BHive Tour

This chapter, along with the launch configuration available in the bhive project, will give a short tour around most of the functionality that bhive provides.

All launch configurations used will use a BHive target in a runtime workspace in the containing workspace (${workspace_loc}/runtime-hive) in case you want to have a look at it.


Import is the act of digesting a folder recursively into a BHive storage. There are two important parameters: the source folder and the destination BHive. Since BHive creates an empty hive automatically in the destination, the target BHive directory is allowed to be non-existant. The source folder is not required to follow any rules at this low-level stage. BHive will simply digest any file found recursively. While doing so, it separates each files content from it’s name. They are stored in separate locations (content as 'blob', name is stored in a 'tree' as 'pointer' to the 'blob' for this file’s content).

Use the Hive-Import launch configuration to import a directory into the BHive. The launch will prompt for two things:

  1. The folder to import. You can choose any folder to import. The target hive is created automatically if it does not exists.

  2. The name (manifest key) of the imported tree. This name can be used to reference the imported tree later on. Note that a name:tag combination must be unique. Import will fail if the manifest key is already used.

Note that all BHive objects are immutable, meaning that there are never changes to any existing file. This is analogous to GIT. Manifests are not BHive objects but more special (they just reference a root tree BHive object). They are mutable in that labels can be added and removed from the manifest.


You can list the content of the BHive after importing by running the Hive-Manifest-List launch configuration. It will simply list all available manifests in the BHive.


The inverse operation of an Import is (surprise) an Export, which means restoring a file/folder tree exactly as it was imported. The export will scan a manifest for 'tree' objects and write all 'blob' objects to the locations described there.

Run the Hive-Export launch configuration and specify a target folder (which may not yet exist). Next specify a manifest to export, use the key you specified during Import.

Check the directory, you will notice that all files have been written back on disc, and the folder content is equal to the one imported.

Remote Serve

BHive provides a small embedded server which allows serving any number of local hives through HTTPS.

Run the Hive-Remote-Serve launch configuration to run the server, serving the BHive created with the Hive-Import application.

Note: the sample launch configurations use the test-only pre-built certificates from the jersey project.

Remote List

The same list operation as before (Hive-Manifest-List) can be performed on the remote server as well, as long as Hive-Remote-Serve is still running.

Run Hive-Remote-List to try it - this will go through the HTTPS stack and perform the manifest listing remotely.

Remote Fetch & Push

The two tools fetch and push allow to fetch and push manifests along with all required objects from and to a remote hive.

Both operations are practically identical, just reversed. To demonstrate fetch, run Hive-Remote-Fetch and specify the manifest key you imported before. This will create a new (empty) hive (on first run) next to the one created by import (${workspace_loc}/runtime-hive-fetched) and fetch this manifest into that hive. Make sure that Hive-Remote-Serve is still running for this to work.

If you are interested, you can try to import another folder which shares some parts with the first one you imported. Due to the separation of content and location, each common file will be stored only once, regardless of it’s location (name) in the tree. This will also enable fetch/push to transfer only missing objects.


The FSCK (short for 'filesystem check') will check consistency of all objects and manifests in e BHive. Run Hive-FSCK to execute a FSCK on the sample BHive.


Manifests can be deleted from a BHive as well. Run Hive-Manifest-Delete to delete a manifest. Be sure to give the same manifest key as with Hive-Import.

Note that this operation only deletes the manifest, but not automatically all now-unreferenced objects from the object database. This is done by Prune.


Pruning is a cleanup operation which removes unreferenced objects from the storage. It is comparable to a git gc.

Run Hive-Prune after running Hive-Manifest-Delete to see the effects of pruning remaining objects. If you had only one manifest and deleted that, the result should be that the objects directory in the hive contains no files anymore (only empty directories).

TreeSnapshot & Co.

The ScanOperation allows to fetch a TreeSnapshot of a MANIFEST root tree. This allows to recursively retrieve all available/relevant information about a MANIFEST. This includes a listing of TREE, BLOB, MREF, missing/damaged objects, etc.

The TreeDiff allows to compare two TreeSnapshot objects. It will produce a TreeElementDiff for each element which is different in the two snapshots. This diff is based on the type and checksum of the according path entries in the snapshots. There is no actual content diff, but it is 'ease' to build one based on the available information.

PCU (Process Control Unit)

The PCU consumes a pre-rendered (meaning all parameter value variables are resolved, all paths are absolute, etc.) configuration to control and run locally.

The PCU does not make any assumptions about locations, etc. It relies completely on external sources to prepare a ProcessGroupConfiguration and the according ProcessConfiguration per configured application.

DCU (Deployment Control Unit)

The DCU’s InstanceNodeController is responsible for consuming an InstanceNodeManifest. An InstanceNodeManifest is an artificial BHive manifest created by a configuration application, typically the web UI.

The DCU assumes that any referenced BHive MANIFEST is locally available, i.e. has been pushed to the BHive associated with the DCU before passing a reference to it to the DCU.

Note that the DCU does not know about multiple nodes in a system. It assumes that everything is local, and so do all data structures in the DCU. The minion controlling the local DCU may have additional higher level structures to allow multiple DCUs distributed among nodes deploying for a single InstanceManifest.


Right now, there is only a single DCU, which has the nodes physical disc as manifestation target.

The architecture is designed in a way to be able to later on have plug-able DCUs, which assume responsibility for a certain node type. This allows to implement specific DCUs later and mix and match them on a node level. For instance a special "Kubernetes" node could allow to drop applications into a cluster, having the cluster side-by-side with classic local application installation (but sharing configuration data, …​).


This bundle contains things shared by all components (BHive, DCU, PCU, Minion, …​).


The io.bdeploy.common.security package contains the SecurityHelper which can be used to generate and verify keystores and access tokens for remote APIs (over HTTP).


The io.bdeploy.common.cfg package contains the Configuration class which can be used to create command line tools and map their parameters to annotation proxies.


The ActivityReporter implementations (Stream and Null) can be used to track activities/operations.


The io.bdeploy.common.metrics package contains an entry point to allow measurement of various metrics.


  1. The JUnit5 @RegisterExtension annotation allows to register instances of extensions (as opposed to @ExtendWith, which registers a class and manages it’s lifecycle as apropriate). This means that the instance does not changed. This on the other hand means that the instance fields of this extension will keep their state throughout test methods. This is not dramatic, just something you need to be aware of. This is the reason why TestMinion calls resetRegistrations() in it’s beforeEach method. Not doing so led to duplicate registrations of singleton services, where the server picked up the services for another test later on…​

Minion (master/slave) Server

The minion is the main BDeploy deliverable. It contains all the command tools as well as the server for remote services and the configuration web UI.

Use bdeploy init …​ to initalize a minion root, then use either bdeploy master …​ or bdeploy slave…​ to launch a master (including web UI) or a slave (controlled by a master) from that root

Client Launcher

The client launcher picks up .bdeploy files passed on the command line and handles application download/synchronization with the origin server, as well as installation in a cache directory and launching of the installed application(s).


Model Class Naming

The classes in this project follow a strict naming scheme.

Class Name Suffix Meaning


Things which are provided by the 'outside' world to describe artifacts processed by us.


Holds data generated by us, based on *Descriptors, user input, or even thin air.


Wraps and manages storage of *Configurations in the underlying BHives. Also handles enumeration/scanning for according objects in the BHive(s).


(not actually in the interfaces project, but ui specific). Holds/groups data which is required in this form for user display/interaction in the UI.


Interfaces for remote (JAX-RS) resources.


Providers for variable expansion in configurations on the target system.

Variable Expansion

This project contains the logic for resolving variables when deploying to a minion. The following schemes are supported.

Expansion of variables happens for launcher paths and parameter values. Additionally, all configuration files are post-processed on the target to perform the exact same expansion.

Provider Variable Pattern Supported Values Example Description



  • APP: (optional) The name of the application to reference. If not given, the parameter is referenced within the same application as the referencing parameter

  • PARAM: The name of the parameter


Expand the value of another parameter inline into the value of this parameter.



  • CONFIG: directory where all configuration files will be placed by deployment

  • BIN: directory where all binaries are placed by deployment

  • RUNTIME: directory with runtime data (e.d. stdout/stderr capture files)

  • DATA: persistent data directory - the only directory shared by multiple deployments of the same instance.


Expand one of the special directories (see SpecialDirectory) know by the deployment process.



  • SYSTEM_PURPOSE: the purpose of the instance, see InstancePurpose

  • UUID: UUID of the instance

  • NAME: name of the instance

  • PRODUCT_ID: name of the MANIFEST key’s name of the configured product

  • PRODUCT_TAG: the tag (i.e. 'version') of the configured product


Expand values related to the instance containing the parameter’s process



  • MANIFEST_NAME: the name of the manifest to reference. The variable will expand to the installation path of that other manifest.

  • TAG: (optional) if given expand to the exact manifest version.


Expand the absolute installation path to another manifest’s path on the target system.



  • OSNAME: either OperatingSystem value (WINDOWS, LINUX, AIX).

  • VALUE: the target value to expand if the target OS matches the OSNAME value.


Insert the given VALUE if and only if the given OSNAME (see OperatingSystem) matches.



  • HOSTNAME: expands to the hostname of the target minion where the application is deployed.


Expands to target minion properties - currently only HOSTNAME is supported.


Almost all of BDeploy's storage is encapsulated in Manifests in a BHive. This holds true not only for actual application/product data, but for any configuration data as well. These have a few advantages over traditional storage:

  • Contents is immutable

  • Contents is validatable (through checksums)

  • Contents is automatically versioned

  • Contents history is available

There are a bunch of Manifests for several purposes.

Special Manifest Types
Manifest Name Purpose


Stores information (name, description, logo) related to an Instance Group. There is exactly one InstanceGroupManifest per Instance Group BHive.


Stores information (name, description) related to a Software Repository. There is exactly one SoftwareRepositoryManifest per Software Repository BHive.


The InstanceManifest holds information about an instance and keeps track of the all InstanceNodeManifest for the Instance.


Keeps track of the Applications and their configuration per configured Node in the Instance. A Node always corresponds to a registered Slave on the target Master.


Holds information about a product and keeps track of all the ApplicationManifest for the Product.


Holds information about a single application, includes the app-info.yaml for the application which holds information about all supported parameters, etc.


Holds information about available slaves on a master.


Manages special per-user Manifests which hold information about each user.


In addition to traditional Manifest there are MetaManifest. These allow to attach certain information to other Manifests. This allows to update the attached MetaManifest independently of the immutable Manifest, whilst keeping all benefits of a Manifest for the MetaManifest as well (versioning, history, …​).

MetaManifest Name Purpose


Keeps track of Instance state related information (installed Instance versions, activated Instance version, etc.).


Keeps track of the history of an Instance version, storing timestamps at which certain actions happened (creation, installation, activation, etc.).


Keeps track of attached managed masters on a central master.


Keeps track of the responsible controlling master for a single Instance.

UI Front- and Backend

Contains the angular configuration frontend as well as the matching backend.


The app-theme.scss currently supports a dark and a light theme. Components can contribute their own themes using SCSS mixins. This has the advantage that the component theme can access theme colors without knowing their exact definition. Whether the theme is dark or light (generally speaking) can be queried, so defining new (own) colors can be made dependent on that.

To create a theme mixin for any component:

  • Create a new .scss file in the component’s folder, e.g. my-component.scss.

  • Import angular material theming support

  • Define a mixin with your theme selectors (attention, those are application global, so be careful with naming them).

  • Import and include the new mixin in the global app-theme.scss

A very simple custom component’s scss file could look like this:

@import '~@angular/material/theming';

@mixin my-component-theme($theme) {
  .my-component-class {
  	background-color: mat-color(map-get($theme, warn));

This will create a CSS class using the current themes 'warn' color as background.

Now you need to include and import the theme in the global app-theme.scss file:

@import '~@angular/material/theming';
@include mat-core();

/* Custom component theme collection */
@import 'app/my-component/my-component-theme.scss';
@import ... (other component themes)

@mixin all-themes($theme) {
  // general angular material theme
  @include angular-material-theme($theme);

  // application themes
  @include my-component-theme($theme);
  @include ... (other component themes)

... (rest of file)

Accessing theme properties in a mixin

Angular material defines a few properties. Those can be accessed from within a mixin easily. Basically a SCSS selector/mixin is just a map, so map-get can be used to access the actual values.

@import '~@angular/material/theming';

@mixin my-component-theme($theme) {
  $dark: map-get($theme, is-dark);

  $color-light: rgb(230, 255, 230);
  $color-dark: rgb(42, 56, 42);

  .my-component-class {
    background-color: if($dark, $color-dark, $color-light);

As you can see the is-dark property of the theme is queried here. If the value is true, $color-dark is used, otherwise $color-light is used.

Available attributes are:

  • primary - the primary palette, can be used with mat-color

  • accent - the secondary palette, can be used with mat-color

  • warn - the warn palette, can be used with mat-color

  • is-dark - boolean determining whether the theme is dark or light.

  • foreground - complex map containing various foreground colors.

  • background - complex map containing various background colors.


Every theme has a primary, accent and warn palette. You can access those colors using mat-color.

@mixin my-component-theme($theme) {
  $accent-palette: map-get($theme, accent);

  $bg-color-lighter: mat-color($accent-palette, lighter);
  $bg-color-normal: mat-color($accent-palette);
  $bg-color-darker: mat-color($accent-palette, darker);

  .my-component-class {
  	background-color: $bg-color-lighter;

mat-color accepts a palette as argument. This can be either of the theme palettes. An optional second argument can be either lighter, darker or a dedicated index into the palette to choose a certain color intensity explicitly.

Foreground Colors

The complex foreground map has the following named color definitions:

  • base

  • divider

  • dividers

  • disabled

  • disabled-button

  • disabled-text

  • elevation

  • hint-text

  • secondary-text

  • icon

  • icons

  • text

  • slider-min

  • slider-off

  • slider-off-active

Each of those can be accessed by map-get-ting them:

@mixin my-component-theme($theme) {
  $background-colors: map-get($theme, background);

  .my-component-class {
  	background-color: map-get($background-colors, app-bar);

This example will use the app-bar map key in the complex background map entry of the current theme.

Background Colors

Analogous to foreground colors, these background colors are defined.

  • status-bar

  • app-bar

  • background

  • hover

  • card

  • dialog

  • disabled-button

  • raised-button

  • focused-button

  • selected-button

  • selected-disabled-button

  • disabled-button-toggle

  • unselected-chip

  • disabled-list-option

Using these foreground colors works exactly the same as background colors do.

Development Setup

BDeploy uses the Eclipse IDE for backend- and VSCode for frontend-development. You will need:

Environment Setup

  • You will want to set the JAVA_HOME environment variable to point to the path where you extracted the OpenJDK 11 package to assure that the build picks up the correct Java.

  • Make sure that the npm command works from the command line where you will run gradle builds (cmd.exe on Windows, bash on Linux).

  • Install the Angular CLI globally for easier working by running npm install -g @angular/cli.

You need root permissions on Linux if you installed NodeJS (and NPM) through your distribution to be able to globally install the Angular CLI.

Repository and Gradle Build

This documentation will assume the path /work/bdeploy to be available, if not substitute it with any other path that works for you.

  • Clone the repository: cd /work/bdeploy && git clone https://github.com/bdeployteam/bdeploy.git

  • Change to the repository directory: cd bdeploy

  • Start the gradle build

    • ./gradlew build on Linux (bash)

    • .\gradlew.bat build on Windows (cmd.exe)

    • The build should conclude with a BUILD SUCCESSFUL message

The gradle build will build test and package BDeploy. You can find build artifacts after the build here:

  • ./launcher/build/distributions - Distributable packages of the launcher application which is used to start client applications.

  • ./minion/build/distributions - Distributable packages of the main BDeploy binaries. They contains the master and slave server commands as well as all CLI commands available to BDeploy Administrators. The distribution also contains all supported launcher packages as nested ZIP files.

  • ./interfaces/build/libs/bdeploy-api-*-all.jar - The distributable API bundle including all external dependencies. This can be used to create additional integrations for BDeploy.

Additionally, documentation deliverables can be found in the ./doc/build/docs/dev and ./doc/build/docs/user directories (developer and end-user documentation respectively).

Eclipse Workspace

To be able to build, start and debug BDeploy backend applications from the Eclipse IDE, you need to perform some extra setup steps:

  • On the command line (see Repository and Gradle Build) generate the Eclipse IDE project files by running ./gradlew eclipse (gradlew eclipse on windows).

  • Start the Eclipse IDE - choose a workspace, e.g. /work/bdeploy/workspace.

  • Open the Git Repositories view.

  • Click Add existing local repository, browse to the repository location (e.g. /work/bdeploy/bdeploy) and add it.

  • Right click the repository in the Git Repositories view and select Import Projects…​.

    • Select all projects with type Eclipse project

    • Don’t select the projects in the eclipse-tea folder.

    • Don’t select projects of type Maven.

This results in a complete BDeploy workspace setup which compiles automatically.

Running BDeploy from Eclipse

BDeploy uses LcDsl launch configurations to run binaries. You can find launch configurations in the Launch Configurations view.

  • Find and run (hint: right click) the Master-Init launch configuration.

    • This will initialize a BDeploy master root inside the chosen workspace directory, e.g. /work/bdeploy/workspace/runtime/master.

    • A default user will be created: username = admin, password = admin.

  • Finally find and run the Master launch configuration to spin up a BDeploy master.

The BDeploy master will host the Web UI also when started from the Eclipse IDE, but it will not work due to slightly different setup. You must use VSCode to host a matching Web UI for the backend run from Eclipse.

Running BDeploy’s Web UI from VSCode

To spin up a matching frontend for the master started in Running BDeploy from Eclipse you need to start the Angular application from within VSCode.

  • On the command line, navigate the the ./ui/webapp directory in the repository (e.g. /work/bdeploy/bdeploy/ui/webapp) and run VSCode in the current directory using code .

  • Open a terminal in VSCode and run ng serve to start the Angular development server. This will take a while to compile the Web UI.

    • The terminal can be opened using Terminal  New Terminal.

    • The application will be started at http://localhost:4200 by default.

BDeploy’s backend is HTTPS only. It uses a self-signed certificate by default. This will require to accept the certificate in the browser before any communication (especially from within the Web UI) can happen.

This makes it necessary to open a second tab in the browser and navigate to https://localhost:7701 to accept the security exception before the Web UI can communicate with the backend properly. Note that this URL will also load the Web UI once the security exception is in place, but will fail to start (see note above).

Building for other platforms

You can build distribution packages for other platforms by installing their respective JDKs. You need to specify those JDKs as properties during the build. To simplify the process, you can create these entries in ~/.gradle/gradle.properties:

Of course you need to download those JDKs and adapt the paths to your environment.


BDeploy has plugin support, for now mainly to contribute custom parameter editors, for example to contribute an encryption algorithm to a password input field, etc.

From a low level viewpoint, plugins (as of now) may:

  • Contribute JAX-RS endpoints to the server side. These endpoints are provided in a dedicated JAX-RS application on the server, so basically all kinds of Providers, Features, Filters and Resources can be registered on the plugins behalf.

  • Contribute static assets. Those are served from a dedicated location per-plugin, and can host all kinds of static resources, including the required ES6 JavaScript modules used to provide custom editor UI.

  • Define custom editors and provide the matching ES6 module through the static resources mentioned above.

1 The server will first load any global plugins that are installed. When loading a plugin, it is internally registered and a dedicated namespace is assigned where resources are served. The server will register the plugins JAX-RS endpoints and all static assets provided by the plugin under this context path. They are then directly accessible from the outside.
2 The Web UI will query for available custom editors once a parameter specifies it requires one (see app-info.yamlcustomEditor in the end user documentation).
3 The Web UI’s plugin service will query the backend for plugins which can provide the requested editor(s). This will also demand-load plugins which are provided by the product backing the instance currently being edited. This works the same as for global plugins above.
4 Assuming the backend returned a plugin providing a suitable custom editor, the custom editor metadata includes the path to the JavaScript (ES6) module to load. The module is loaded into the Web application.
5 Then it is instantiated and passed an API object which can be used to transparently access the plugins exposed resources (JAX-RS API, static assets).
6 The custom editor is bound to the Web UI on demand and can now perform edit operations on parametes, using its backend resources as required.

Plugin Distribution

Plugins are distributed and loaded in two ways:

  • A global plugin is a JAR file which is added to the server either through the command line or its UI. Global plugins provide functionality to be used by everything on the server globally on demand.

  • A product-bound (local) plugin is delivered through the product by configuring it in the product-info.yaml. See the user documentation for details.

How to create a plugin

A template to begin from is provided in the GitHub repository. It contains all the bits required:

  • A plugin project must compile against the BDelpoy API JAR. This can be found either in the GitHub packages Maven repository, or on the releases page as plain JAR.

  • A plugin must extend io.bdeploy.api.plugin.v1.Plugin class. It may override methods to provide its resources to BDeploy.

  • A plugin must specify some important MANIFEST.MF headers which help the BDeploy plugin system with identifying plugins:

    • BDeploy-Plugin: This header should contain the fully qualified class name of the class extending the io.bdeploy.api.plugin.v1.Plugin class.

    • BDeploy-PluginName: A human readable name for the plugin helping administrators identifying the plugin.

    • BDeploy-PluginVersion: A version string, helping administrators identifying the plugins version.

  • A plugin can contain JAX-RS resource for the backend

  • A plugin can contain ES6 JavaScript modules which provide custom editor UI for the user. In theory, you can use whatever you like, as long as it has a single JavaScript entrypoint file which can be loaded from the UI (e.g. Stencil WebComponents have been tested - you still need to provide the single entrypoint class though).

    • The ES6 module must contain a default exported class, so BDeploy can instantiate the plugin withough knowing its class names.

The JavaScript Plugin API

The Java API is pretty straight forward, and can be seen immediately when looking at the io.bdeploy.api.plugin.v1.Plugin class. It is a little bit different for the JavaScript API, as there are no interfaces you can look at. Internally, BDeploy uses TypeScript and thus it has an interface definition.

The Custom Editor API

The interface for a custom editor looks like this:

export interface EditorPlugin {
  new(api: Api); (1)
  bind(onRead: () => string, onUpdate: (value: string) => void, onValidStateChange: (valid: boolean) => void): HTMLElement; (2)

A custom editor definiton in the plugins main class points to an ES6 module, whos default class must implement this interface.

1 The constructor accepts an API object, which can be used to interface with the JAX-RS resources of the plugin.
2 The bind method receives callbacks for communication with the configuration web UI, and returns an HTMLElement which has to be created by the plugin.

The API Object

The API Object is passed to the plugins constructor. It allows communication with the plugins backend, without the need for the plugin to know where exactly this API is hosted on the server.

export interface Api {
  get(path: string, params?: {[key: string]: string}): Promise<any>(1)
  put(path: string, body: any, params?: {[key: string]: string}): Promise<any>;
  post(path: string, body: any, params?: {[key: string]: string}): Promise<any>;
  delete(path: string, params?: {[key: string]: string}): Promise<any>;
  getResourceUrl(): string; (2)
1 The get, put, post and delete methods can be used to issue according requests to the plugins JAX-RS resources.
2 The resource URL can be used to load static resources. The URL will be the base URL where static and JAX-RS resources are registered.