Create an experiment object for the subject and image group. Objects
        are referenced by their identifier. The reference to a functional data
        object is optional.

        Raises ValueError if no valid experiment name is given in property list.

        Parameters
        ----------
        subject_id : string
            Unique identifier of subject
        image_group_id : string
            Unique identifier of image group
        properties : Dictionary
            Set of experiment properties. Is required to contain at least the
            experiment name
        fmri_data_id : string, optional
            Unique identifier of functional MRI data object

        Returns
        -------
        ExperimentHandle
            Handle for created experiment object in database

def create_object(self, subject_id, image_group_id, properties, fmri_data_id=None):
        """Create an experiment object for the subject and image group. Objects
        are referenced by their identifier. The reference to a functional data
        object is optional.

        Raises ValueError if no valid experiment name is given in property list.

        Parameters
        ----------
        subject_id : string
            Unique identifier of subject
        image_group_id : string
            Unique identifier of image group
        properties : Dictionary
            Set of experiment properties. Is required to contain at least the
            experiment name
        fmri_data_id : string, optional
            Unique identifier of functional MRI data object

        Returns
        -------
        ExperimentHandle
            Handle for created experiment object in database
        """
        # Ensure that experiment name is given in property list.
        if not datastore.PROPERTY_NAME in properties:
            raise ValueError('missing experiment name')
        elif properties[datastore.PROPERTY_NAME] is None:
            raise ValueError('invalid experiment name')
        # Create a new object identifier.
        identifier = str(uuid.uuid4()).replace('-','')
        # Create object handle and store it in database before returning it
        obj = ExperimentHandle(
            identifier,
            properties,
            subject_id,
            image_group_id,
            fmri_data_id=fmri_data_id
        )
        self.insert_object(obj)
        return obj