Build custom resources

This page describes how to build custom recognition resources to fine-tune the recognition.

How to build resources

This is a two-step process: You should first prepare a resource file. This file is a UTF-8-encoded file containing dedicated resources information.

For Text recognition, possible resources are lexicon and subset knowledge. Lexicon files should have a .txt or a .lex extension, whereas subset knowledge files should have a .txt or a .sk one.

For Math recognition, you can set up your math grammar defining the symbols and rules. They shall be saved in a .txt or .def file.

Once you have writen your resource file, you must compile it to generate the corresponding binary .res file.

How to compile resources

Via the Developer Portal

MyScript Developer Portal comes with an online tool that lets you compile your own resources files.


Interactive Ink SDK also comes with a built-in tool to generate text lexicons and math grammars (respectively choose "Text Lexicon" and "Math Grammar" as the target asset type).

The workflow is as follows:

  1. Create a RecognitionAssetsBuilder object from your engine.
  2. Call its compile() method, passing it the right information.
  3. Serialize the resource into a file using the store() method.

  4. Reference the new resource in your configuration file
  5. Update your engine or editor configuration if needed (it may not be needed if you keep the same configuration bundle and name)
  6. Create a new part and associate it with an editor
It is important to update the configuration before creating a new part and attaching it to an editor, as the configuration name attached to the part will be set at that time and cannot be changed afterwards.

For example, to compile a math grammar, steps 1 to 3 will look as follows:

// 1. Create a recognition assets builder
RecognitionAssetsBuilder assetsBuilder = engine.createRecognitionAssetsBuilder();
// 2. Define and compile the grammar
String grammar = "...";
assetsBuilder.compile("Math Grammar", grammar);
// 3. Save it to the disc
String internalStoragePath = getBaseContext().getFilesDir().getPath();
File file = new File(internalStoragePath, File.separator + "customised-grammar.res");;

Step 4 consists in editing our math configuration (or create a new one) to load our custom grammar instead of the standard one:

AddResource math/custom-grammar.res
Make sure that the path to the resource is correct.

You can get the list of recognition assets types that can be compiled via the getSupportedRecognitionAssetsTypes() method of the RecognitionAssetsBuilder object.



The lexicon is a list of words or expressions that is being used by the engine to recognize a specific set of terms. You can create your own lexicon to improve the recognition. It may contain terms that are unlikely to appear in a classical dictionary but that you will be led to write many times (proper nouns like the name of your company or your employees, your password, a hashtag, etc.).

For example, a lexicon can be the following set:


If needed, you can also download another Lexicon example.

You can attach several lexicons to a configuration to complement or replace the MyScript-provided LK.

Subset knowledge

The Subset Knowledge resource (or SK) is a white list that works as a filter to constrain the recognition to a specific set of characters. You can create your own SK to improve the recognition and help the engine reduce the “margin of error”. The expected set can be limited to digits or to letters in a given alphabet or language.

For example: In a form field where you expect a phone number, constraining the recognition with a SK could avoid the engine to mistake a “0” for a “O” or a “1” for a “l”.

See below examples of SK resources:


If needed, you can download another SK example.


Grammar resource

The grammar resource indicates the way to parse handwritten mathematical expressions. It specifies:

  • a limited set of terminal symbols,
    Terminal symbols are the elementary symbols. They are basic symbols such as a, b, c, …, 0, 1, …, +, -, ±, etc. that cannot be broken down into “smaller” recognized units. See below the list of supported symbols.

  • a limited set of non-terminal symbols,
    Non-terminal symbols describe groups of terminal symbols organized according to rules.

  • a limited set of rules,
    Rules describe the way to parse digital ink. For instance, a fraction is a rule that contains a numerator, a fraction bar and a denominator. The recognizer expects to find these three elements to fit the fraction rule. See below the list of supported rules.

  • a start symbol.
    This defines the way your mathematical expression should be read depending on the above elements.

For example, a grammar resource can be:

symbol = 0 1 2 3 4 5 6 7 8 9 + - / ÷ = . , % | ( ) : * x
leftpar = (
rightpar = )
currency_symbol = $ R € ₹ £
character ::= identity(symbol)
            | identity(currency_symbol)
fractionless ::= identity(character)
               | fence (fractionless, leftpar, rightpar)
               | hpair(fractionless, fractionless)
fractionable ::= identity(character)
               | fence (fractionable, leftpar, rightpar)
               | hpair(fractionable, fractionable)
               | fraction(fractionless, fractionless)
expression ::= identity(character)
             | fence (expression, leftpar, rightpar)
             | hpair(expression, expression)
             | fraction(fractionable, fractionable)

If needed, you can download another Grammar example.

You can only attach one grammar per configuration.

Grammar syntax

You can build your own MyScript-Math-compliant grammar resource. To do so, you must define the grammar in conformity with the syntax set out below and then compile it.

You can add comments in a grammar resource as follows:

// This is the first way to start a whole comment line.
#  This is the second way to start a whole comment line.
"  This is the third way to start a whole comment line.
/* This is a block comment. */

Inline comments are not supported.

Your grammar resource will contain terminal symbol definitions such as the following:

my_terminal_name = 0 1 2 3 4 5 6 7 8 9
  • The terminal symbol name is defined as: [-a-zA-Z_][-a-zA-Z_0-9]
    It is a character string which starts with a character from [-a-zA-Z_] and whose other characters are any of [-a-zA-Z_0-9]. In the above example, the terminal symbol name is my_terminal_name.

  • The list of symbols referred to by the terminal name are defined as: ( ( !EOL . )+ | EOL space+ )+
    The definition of the symbols referred to by the terminal name does not start by a EOL (end of line). They can be any existing character separated by a space or EOL and a space. In other words, the definition of the symbols is allowed to span multiple lines, providing that the “continuation line” starts with a space. This means you can format long terminal symbol definitions in a more visually organized (“pretty-formatted”) manner. In the above example, the list of symbols referred to by my_terminal_name is 0 1 2 3 4 5 6 7 8 9.

  • Space is defined as ‘ ’ or ‘\t’

  • EOL is defined as ‘\r\n’ or ‘\n’ or ‘\r’

You will also need to list non-terminal symbol definitions. Here is an example:

my_non_terminal_name ::= fraction(my_terminal_name,my_terminal_name)
  • The non-terminal symbol name is defined as : [-a-zA-Z_][-a-zA-Z_0-9]
    It is a character string which starts with a character from [-a-zA-Z_] and whose other characters are any of [-a-zA-Z_0-9]. In the above example, the non-terminal symbol name is my_non_terminal_name.

The non-terminal symbol is defined as: non_terminal_name ::= rule (| rule)?

In the above example, the rule is fraction. The example specifies that the numerator is a my_terminal_name symbol and that the denominator is also a my_terminal_name symbol.

Putting this example aside, note that MyScript Math also offers the possibility to recognize “partial” fraction, i.e. with one denominator only or with one numerator only. This feature is available by default, so that you do not need to add a non-terminal entry to recognize “partial” fractions.

Rule continuations allow you to “pretty format” rule definitions by avoiding a repetition of target non-terminal symbol names.

Finally, your grammar must include the start symbol definition:


Finally, you must define the start symbol. In the above example, we specify that the general mathematical expression form that will be recognized is my_non_terminal_name. In other words, we expect the input digital ink to represent a fraction of digits.

Here is an example of a custom grammar:

Terminal symbol Non-terminal symbol Rule Start symbol start (expression) symbol 0 1 2 3 4 5 6 7 8 9 a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z + - = / x ÷ ± √ identity (symbol) | hpair (expression, expression) expression ::= | fraction (expression, expression) | sqrt (expression) | superscript (symbol, expression)

Supported symbols and rules

A non-exhaustive list of supported math symbols and rules can be found here.

It is also possible to create a custom grammar resource, by constraining the recognition for particular use cases (integral calculus, vector calculus, finite element calculus, etc.).

The following table provides for each supported math rule its denomination in the grammar as well as the parameters it supports:

Rule Visual structure Syntax Explanation
Identity N/A identity(source) Reuse a previously defined symbol in a rule clause
Horizontal pair hpair(left, right) Ordered juxtaposition of the left and right expressions
Fence { } [ ] ( ) fence(exp, left, right) exp is placed between the left and right symbols
Left fence leftfence(exp, symbol) symbol is positioned at the left of exp. This allows for instance defining systems
Square root sqrt(exp) exp is placed under the square root
Fraction fraction(numerator, denominator) numerator is divided by denominator
Subscript subscript(exp, index) index is placed as subscript at the right of exp
Superscript superscript(exp, exponent) exponent is placed as superscript at the right of exp
Subsuperscript subsuperscript(exp, index, exponent) index and exponents are respectively placed as subscript and superscript at the right of exp
Presuperscript presuperscript(exp, exponent) exponent is placed as superscript at the left of exp
Presubscript presubscript(exp, exponent) exponent is placed as subscript at the left of exp
Overscript overscript(exp, top) top is placed above exp
Underscript underscript(exp, bottom) bottom is placed as subscript at the left of exp
Underoverscript underoverscript(exp, bottom, top) top and bottom are respectively placed as superscript and subscript at the left of exp
Vertical pair vpair(top, bottom) top and bottom are respectively placed one on top of the other
Vertical list vlist(exp) exp represent the expressions that can be placed on several consecutive lines
Table table(exp) exp represent the expressions that can be placed inside the table cell. This allows for instance defining matrices
Partial fraction (numerator) partialfractionnumerator(numerator) Only the numerator of the fraction is defined
Partial fraction (denominator) partialfractiondenominator(denominator) Only the denominator of the fraction is defined
Slanted fraction slantedfraction(numerator, denominator) numerator is divided by denominator

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