content/api/user-guide/4.2.1.9-apacheds-schema-elements.mdtext

Title: 4.2.1.9 - ApacheDS Schema Element
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# 4.2.1.9 - ApacheDS Schema Element

We have defined 3 more schema elements that are needed to use the **SchemaManager**:
* SyntaxChecker : used to check a value's syntax
* Normalizer : used to normalize a value before a comparison
* LdapComparator : used to compare two values for a given syntax

## SyntaxChecker

This class exposes this method:

* isValidSyntax(Object): tells if the value is correct

## Normalizer

This class is used to normalize values into a canonical form. This is a process exposed in [RFC4518|https://tools.ietf.org/html/rfc4518]. Basically, each String is passed trhough a 6-step process:

* Transcode
* Map
* Normalize
* Prohibit
* Check Bidi (Bidirectional)
* Insignificant Character Handling

This can be done using one of these two methods:

* normalize(String) : normalize a String
* normalize(Value<?>) : normalize a Value, which can be a String or a byte[]

This class is used internally when comparing two values, but you should not need it.

## LdapComparator

This class is used to compare two values whenever their syntax are the same. Here is the method that does it:

* equals(Object) : says if a value is equal to another one.

Note because the **LdapComparator** class implements the **Comparator** interface, one can compare two values using the following method:

* compare( v1, v2 ): compares two values