<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def GetDefinitionByName(self, name):
 """Retrieves a specific data type definition by name. Args: name (str):
 name of the data type definition. Returns: DataTypeDefinition: data type definition or None if not available. """

    lookup_name = name.lower()
    if lookup_name not in self._definitions:
      lookup_name = self._aliases.get(name, None)

    return self._definitions.get(lookup_name, None)