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Custom Link Types


Requirements Management Interface (RMI) provides legacy functionality. Starting in R2022a, use slreq.refreshCustomizations. For more information, see Define Custom Requirement and Link Types by Using sl_customization Files.

Create a Custom Requirements Link Type

In this example, you implement a custom link type to a hypothetical document type, a text file with the extension .abc. Within this document, the requirement items are identified with a special text string, Requirement::, followed by a single space and then the requirement item inside quotation marks (").

You will create a document index listing all the requirement items. When navigating from the Simulink® model to the requirements document, the document opens in the MATLAB® Editor at the line of the requirement that you want.

To create a custom link requirement type:

  1. Write a function that implements the custom link type and save it on the MATLAB path that has these contents:

    function linkType = rmicustabcinterface
    %RMICUSTABCINTERFACE - Example custom requirement link type
    % This file implements a requirements link type that maps 
    % to "ABC" files.
    % You can use this link type to map a line or item within an ABC
    % file to a Simulink or Stateflow object.
    % You must register a custom requirement link type before using it.
    % Once registered, the link type will be reloaded in subsequent
    % sessions until you unregister it.  The following commands
    % perform registration and registration removal.
    % Register command:   >> rmi register rmicustabcinterface
    % Unregister command: >> rmi unregister rmicustabcinterface
    %  Copyright 1984-2010 The MathWorks, Inc.
        % Create a default (blank) requirement link type
        linkType = ReqMgr.LinkType;
        linkType.Registration = mfilename;
        % Label describing this link type
        linkType.Label = 'ABC  file (for demonstration)';
        % File information
        linkType.IsFile = 1;
        linkType.Extensions = {'.abc'};
        % Location delimiters
        linkType.LocDelimiters = '>@';
        linkType.Version = '';             % not required
        % Uncomment the functions that are implemented below
        linkType.NavigateFcn = @NavigateFcn;
        linkType.ContentsFcn = @ContentsFcn;
    function NavigateFcn(filename,locationStr)
        if ~isempty(locationStr)
            case '>'
                lineNum = str2num(locationStr(2:end));
                openFileToLine(filename, lineNum);
            case '@'
                openFileToLine(filename, 1);
    function openFileToLine(fileName, lineNum)
        if lineNum > 0        
            if matlab.desktop.editor.isEditorAvailable
                matlab.desktop.editor.openAndGoToLine(fileName, lineNum);
    function openFileToItem(fileName, itemName)
        reqStr = ['Requirement:: "' itemName '"'];
        lineNum = 0;
        fid = fopen(fileName);
        i   = 1;
        while lineNum == 0
            lineStr = fgetl(fid);
            if ~isempty(strfind(lineStr, reqStr))
                lineNum = i;
            if ~ischar(lineStr), break, end;
            i = i + 1;
        openFileToLine(fileName, lineNum);
    function [labels, depths, locations] = ContentsFcn(filePath)
        % Read the entire file into a variable
        fid = fopen(filePath,'r');
        contents = char(fread(fid)');
        % Find all the requirement items
        fList1 = regexpi(contents,'\nRequirement:: "(.*?)"','tokens');
        % Combine and sort the list
        items = [fList1{:}]';
        items = sort(items);
        items = strcat('@',items);
        if (~iscell(items) && length(items)>0)
         locations = {items};
         labels = {items};
         locations = [items];
         labels = [items];
        depths = [];
  2. To register the custom link type ABC, type the following MATLAB command:

    rmi register rmicustabcinterface

    The ABC file type appears on the Outgoing Links Editor drop-down list of document types.

  3. Create a text file with the .abc extension containing several requirement items marked by the Requirement:: string. Name the file and copy and paste this text in the file:

    Requirement:: "Altitude Climb Control"
    Altitude climb control is entered whenever:
    |Actual Altitude- Desired Altitude | > 1500 
    Actual Altitude - feet
    Desired Altitude - feet
    When the autopilot is in altitude climb 
    control mode, the controller maintains a 
    constant user-selectable target climb rate.  
    The user-selectable climb rate is always a 
    positive number if the current altitude is 
    above the target altitude.  The actual target 
    climb rate is the negative of the user 
    End of "Altitude Climb Control">
    Requirement:: "Altitude Hold"
    Altitude hold mode is entered whenever:
    |Actual Altitude- Desired Altitude | < 
      30*Sample Period*(Pilot Climb Rate / 60) 
    Actual Altitude - feet
    Desired Altitude - feet
    Sample Period - seconds
    Pilot Climb Rate - feet/minute
    The transition from climb mode to altitude 
    hold is based on a threshold that is 
    proportional to the Pilot Climb Rate.  
    At higher climb rates the transition occurs 
    sooner to prevent excessive overshoot. 
    End of "Altitude Hold"
    Requirement:: "Autopilot Disable"
    Altitude hold control and altitude climb 
    control are disabled when autopilot enable 
    is false.
    Both control modes of the autopilot 
    can be disabled with a pilot setting.
    ENd of "Autopilot Disable"
    Requirement:: "Glide Slope Armed"
    Glide Slope Control is armed when Glide 
    Slope Enable and Glide Slope Signal 
    are both true. 
    Glide Slope Enable - Logical
    Glide Slope Signal - Logical
    ILS Glide Slope Control of altitude is only 
    enabled when the pilot has enabled this mode 
    and the Glide Slope Signal is true.  This indicates 
    the Glide Slope broadcast signal has been 
    validated by the on board receiver. 
    End of "Glide Slope Armed"
    Requirement:: "Glide Slope Coupled"
    Glide Slope control becomes coupled when the control 
    is armed and (Glide Slope Angle Error > 0) and 
     Distance < 10000 
    Glide Slope Angle Error - Logical
    Distance - feet
    When the autopilot is in altitude climb control 
    mode the controller maintains a constant user 
    selectable target climb rate.  
    The user-selectable climb rate is always a positive 
    number if the current altitude is above the target 
    altitude the actual target climb rate is the 
    negative of the user setting. 
    End of "Glide Slope Coupled"
  4. Open the aero_dap3dof model. At the MATLAB command line, enter:

    Close the Apollo Lunar Module Descent Animation.

  5. In the aero_dap3dof model, right-click the Reaction Jet Control subsystem and select Requirements > Open Outgoing Links dialog.

    The Outgoing Links Editor opens.

  6. Click New to add a new requirement link. The Document type drop-down list now contains the ABC file (for demonstration) option.

  7. Set Document type to ABC file (for demonstration) and browse for the file. The browser shows only the files with the .abc extension.

  8. To define a particular location in the requirements document, use the Location field.

    In this example, the rmicustabcinterface function specifies two types of location delimiters for your requirements:

    • > — Line number in a file

    • @ — Named item, such as a bookmark, function, or HTML anchor


    The rmi reference page describes other types of requirements location delimiters.

    The Location drop-down list contains these two types of location delimiters whenever you set Document type to ABC file (for demonstration).

  9. Select Line number. Enter the number 26, which corresponds with the line number for the Altitude Hold requirement in

  10. In the Description field, enter Altitude Hold, to identify the requirement by name.

  11. Click Apply.

  12. Verify that the Altitude Hold requirement links to the Reaction Jet Control subsystem. Right-click the subsystem and select Requirements > 1. “Altitude Hold”.

Create a Document Index

A document index is a list of all the requirements in a given document. To create a document index, MATLAB uses file I/O functions to read the contents of a requirements document into a MATLAB variable. The RMI extracts the list of requirement items.

The example requirements document,, defines four requirements using the string Requirement::. To generate the document index for this ABC file, the ContentsFcn function in rmicustabcinterface.m extracts the requirements names and inserts @ before each name.

For the file, in the Outgoing Links: Reaction Jet Control dialog box, click the Document Index tab. The ContentsFcn function generates the document index automatically.

Implement Custom Link Types

To implement a custom link type:

  1. Create a MATLAB function file based on the custom link type template, as described in Custom Link Type Functions.

  2. Customize the custom link type file to specify the link type properties and custom callback functions required for the custom link type, as described in Link Type Properties.

  3. Register the custom link type using the rmi command 'register' option, as described in Custom Link Type Registration.

Why Create a Custom Link Type?

In addition to linking to built-in types of requirements documents, you can register custom requirements document types with the Requirements Management Interface (RMI). Then you can create requirement links from your model to these types of documents.

With custom link types, you can:

  • Link to requirement items in commercial requirement tracking software

  • Link to in-house database systems

  • Link to document types that the RMI does not support

The custom link type API allows you to define MATLAB functions that enable linking between your Simulink model and your custom requirements document type. These functions also enable new link creation and navigation between the model and documents.

For example, navigation involves opening a requirements document and finding the specific requirement record. When you click your custom link in the content menu of a linked object in the model, Simulink uses your custom link type navigation function to open the document and highlight the target requirement based on the implementation provided. The navigation function you implement uses the available API to communicate with your requirements storage application.

Typically, MATLAB runs an operating system shell command or uses ActiveX® communication for sending navigation requests to external applications.

Alternatively, if your requirements are stored as custom variants of text or HTML files, you can use the built-in editor or Web browser to open the requirements document.

Custom Link Type Functions

To create a MATLAB function file, start with the custom link type template, located in:


Your custom link type function:

  • Must exist on the MATLAB path with a unique function and file name.

  • Cannot require input arguments.

  • Must return a single output argument that is an instance of the requirements link type class.

To view similar files for the built-in link types, see the following files in matlabroot\toolbox\slrequirements\linktype_examples\:


Custom Link Type Registration

Register your custom link type by passing the name of the MATLAB function file to the rmi command as follows:

rmi register mytargetfilename

Once you register a link type, it appears in the Outgoing Links Editor as an entry in the Document type drop-down list. A file in your preference folder contains the list of registered link types, so the custom link type is loaded each time you run MATLAB.

When you create links using custom link types, the software saves the registration name and the other link properties specified in the function file. When you attempt to navigate to such a link, the RMI resolves the link type against the registered list. If the software cannot find the link type, you see an error message.

You can remove a link type with the following MATLAB command:

rmi unregister mytargetfilename

Custom Link Type Synchronization

After you implement custom link types for RMI that allow you to establish links from Simulink objects to requirements in your requirements management application (RM application), you can implement synchronization of the links between the RM application and Simulink using Requirements Toolbox™ functions. Links can then be reviewed and managed in your RM application environment, while changes made are propagated to Simulink.

You first create the surrogate objects in the RM application to represent Simulink objects of interest. You then automate the process of establishing traceability links between these surrogate objects and other items stored in the RM application, to match links that exist on the Simulink side. After modifying or creating new associations in the RM application, you can propagate the changes back to Simulink. You use Requirements Toolbox to implement synchronization of links for custom requirements documents. However, this functionality is dependent upon the automation and inter-process communication APIs available in your RM application. You use the following Requirements Toolbox functions to implement synchronization of links between RM applications and Simulink.

To get a complete list of Simulink objects that may be considered for inclusion in the surrogate module:

[objHs, parentIdx, isSf, objSIDs] = rmi('getObjectsInModel', modelName);

This command returns:

  • objHs, a complete list of numeric handles

  • objSIDs, a complete list of corresponding session-independent Simulink IDs

  • isSf, a logical array that indicates which list positions correspond to which Stateflow® objects

  • parentIdx, an array of indices that provides model hierarchy information

When creating surrogate objects in your RM application, you will need to store objSIDs values – not objHs values – because objHs values are not persistent between Simulink sessions.

To get Simulink object Name and Type information that you store on the RM application side:

[objName, objType] = rmi('getObjLabel', slObjectHandle);

To query links for a Simulink object, specified by either numeric handle or SID:

linkInfo = rmi('getLinks', slObjectHandle)
linkInfo = rmi('getLinks', sigBuildertHandle, m)
% Signal Builder group "m" use case.
linkInfo = rmi('getLinks', [modelName objSIDs{i}]);

linkInfo is a MATLAB structure that contains link attributes. See the rmi function reference page for more details.

After you retrieve the updated link information from your RM application, populate the fields of linkData with the updated values, and propagate the changes to Simulink:

rmi('setLinks', slObjectHandle, linkData)

For an example MATLAB script implementing synchronization with a Microsoft Excel Workbook, see the following:

edit([matlabroot '/toolbox/slrequirements/...

You can run this MATLAB script on the example model slvnvdemo_fuelsys_officereq to generate the Excel® workbook surrogate for the model.