diff --git a/python/obitools3/obidms/capidms.cfiles b/python/obitools3/obidms/capidms.cfiles
index d4f6611..b16f90e 100644
--- a/python/obitools3/obidms/capidms.cfiles
+++ b/python/obitools3/obidms/capidms.cfiles
@@ -6,5 +6,5 @@
 ../../../src/obilittlebigman.c
 ../../../src/obitypes.h
 ../../../src/obitypes.c
-../../../src/private_openat.h
-../../../src/private_openat.c
+../../../src/private_at_functions.h
+../../../src/private_at_functions.c
diff --git a/python/obitools3/obidms/capidms.pxd b/python/obitools3/obidms/capidms.pxd
index 494b2ce..41ff4b7 100644
--- a/python/obitools3/obidms/capidms.pxd
+++ b/python/obitools3/obidms/capidms.pxd
@@ -16,11 +16,11 @@ cdef extern from "obidms.h" nogil:
 
     ctypedef OBIDMS_t* OBIDMS_p 
 
-    OBIDMS_p obi_create_dms(const_char_p name)
+    OBIDMS_p obi_create_dms(const_char_p dms_name)
 
-    OBIDMS_p obi_open_dms(const_char_p name)
+    OBIDMS_p obi_open_dms(const_char_p dms_name)
 
-    OBIDMS_p obi_dms(const_char_p name)
+    OBIDMS_p obi_dms(const_char_p dms_name)
 
     int obi_close_dms(OBIDMS_p dms)
 
diff --git a/python/obitools3/obidms/obidmscolumn/capidmscolumn.cfiles b/python/obitools3/obidms/obidmscolumn/capidmscolumn.cfiles
index f318290..486332a 100644
--- a/python/obitools3/obidms/obidmscolumn/capidmscolumn.cfiles
+++ b/python/obitools3/obidms/obidmscolumn/capidmscolumn.cfiles
@@ -1,5 +1,7 @@
 ../../../../src/obidmscolumn.h
 ../../../../src/obidmscolumn.c
+../../../../src/obidmscolumngroup.h
+../../../../src/obidmscolumngroup.c
 ../../../../src/obidms.h
 ../../../../src/obidms.c
 ../../../../src/obierrno.h
@@ -8,5 +10,5 @@
 ../../../../src/obilittlebigman.c
 ../../../../src/obitypes.h
 ../../../../src/obitypes.c
-../../../../src/private_openat.h
-../../../../src/private_openat.c
+../../../../src/private_at_functions.h
+../../../../src/private_at_functions.c
diff --git a/src/obidms.c b/src/obidms.c
index b2d1da1..2b7a966 100644
--- a/src/obidms.c
+++ b/src/obidms.c
@@ -7,15 +7,20 @@
 
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <dirent.h>
 
 #include "obidms.h"
+#include "obierrno.h"
 
 
-/************************************************************************
+/**************************************************************************
  *
- * D E C L A R A T I O N   O F   T H E  P R I V A T E   F U N C T I O N S
+ * D E C L A R A T I O N   O F   T H E   P R I V A T E   F U N C T I O N S
  *
- ************************************************************************/
+ **************************************************************************/
 
 
 /**
@@ -33,7 +38,7 @@
  * @retvalue NULL if an error occurs
  *
  * ###Error values
- * 		- OBIDMS_MEMORY_ERROR    : something wrong occured during memory allocation.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
  * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
  *
  * @since May 2015
@@ -42,11 +47,11 @@
 static char *build_directory_name(const char *dms_name);
 
 
-/***********************************************************************
+/************************************************************************
  *
- * D E F I N I T I O N   O F   T H E  P R I V A T E   F U N C T I O N S
+ * D E F I N I T I O N   O F   T H E   P R I V A T E   F U N C T I O N S
  *
- ***********************************************************************/
+ ************************************************************************/
 
 static char *build_directory_name(const char *dms_name)
 {
@@ -71,31 +76,31 @@ static char *build_directory_name(const char *dms_name)
 }
 
 
-/*********************************************************************
+/**********************************************************************
  *
- * D E F I N I T I O N   O F   T H E  P U B L I C   F U N C T I O N S
+ * D E F I N I T I O N   O F   T H E   P U B L I C   F U N C T I O N S
  *
- *********************************************************************/
+ **********************************************************************/
 
 int obi_dms_exists(const char* dms_name)
 {
     struct stat buffer;
 	char *directory_name;
-    int exists;
+    int check_dir;
 
 	// Build and check the directory name
     directory_name = build_directory_name(dms_name);
 	if (directory_name == NULL)
 		return -1;
 
-	exists = stat(directory_name, &buffer);
+	check_dir = stat(directory_name, &buffer);
 
 	free(directory_name);
 
-    if(exists == 0)
+    if (check_dir == 0)
         return 1;
-    else // -1
-        return 0;
+    else
+    	return 0;
 }
 
 
@@ -108,7 +113,6 @@ OBIDMS_p obi_create_dms(const char* dms_name)
 	if (directory_name == NULL)
 		return NULL;
 
-
 	// Try to create the directory
 	if (mkdir(directory_name, 0x777) < 0)
 	{
@@ -140,24 +144,26 @@ OBIDMS_p obi_open_dms(const char* dms_name)
 	if (directory_name == NULL)
 		return NULL;
 
-	// try to open the directory
+	// Try to open the directory
 	directory = opendir(directory_name);
-	if (directory == NULL) {
-		switch (errno) {
-		case ENOENT:
-			obi_set_errno(OBIDMS_NOT_EXIST_ERROR);
-			break;
+	if (directory == NULL)
+	{
+		switch (errno)
+		{
+			case ENOENT:
+				obi_set_errno(OBIDMS_NOT_EXIST_ERROR);
+				break;
 
-		case EACCES:
-			obi_set_errno(OBIDMS_ACCESS_ERROR);
-			break;
+			case EACCES:
+				obi_set_errno(OBIDMS_ACCESS_ERROR);
+				break;
 
-		case ENOMEM:
-			obi_set_errno(OBIDMS_MEMORY_ERROR);
-			break;
+			case ENOMEM:
+				obi_set_errno(OBIDMS_MEMORY_ERROR);
+				break;
 
-		default:
-			obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+			default:
+				obi_set_errno(OBIDMS_UNKNOWN_ERROR);
 		}
 		free(directory_name);
 		return NULL;
@@ -165,7 +171,6 @@ OBIDMS_p obi_open_dms(const char* dms_name)
 
 	// Allocate the data structure
 	dms = (OBIDMS_p) malloc(sizeof(OBIDMS_t));
-
 	if (dms == NULL)
 	{
 		obi_set_errno(OBIDMS_MEMORY_ERROR);
@@ -178,15 +183,19 @@ OBIDMS_p obi_open_dms(const char* dms_name)
 	dms->directory = directory;
 
 	free(directory_name);
+
 	return dms;
 }
 
 
 OBIDMS_p obi_dms(const char* dms_name)
 {
-	int exists = obi_dms_exists(dms_name);
+	int exists;
 
-	switch (exists) {
+	exists = obi_dms_exists(dms_name);
+
+	switch (exists)
+	{
 		case 0:
 			return obi_create_dms(dms_name);
 		case 1:
@@ -194,7 +203,6 @@ OBIDMS_p obi_dms(const char* dms_name)
 	};
 
 	return NULL;
-
 }
 
 
diff --git a/src/obidms.h b/src/obidms.h
index 889dde9..aa001df 100644
--- a/src/obidms.h
+++ b/src/obidms.h
@@ -41,12 +41,12 @@ typedef struct OBIDMS {
  *
  * @param dms_name a pointer to a C string containing the name of the database.
  *             The actual directory name used to store the DMS will be
- *             `<name>.obidms`.
+ *             `<dms_name>.obidms`.
  *
  * @return an integer value indicating the status of the database
  * @retvalue 1 the database exist
  * @retvalue 0 the database does not exist
- * @retvalue -1 an error occured
+ * @retvalue -1 an error occurred
  *
  * @see obi_close_dms()
  * @since May 2015
@@ -72,7 +72,7 @@ int obi_dms_exists(const char* dms_name);
  * ###Error values
  * 		- OBIDMS_EXIST_ERROR     : a database with the same name already exists.
  * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
- * 		- OBIDMS_MEMORY_ERROR    : something wrong occured during memory allocation.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
  *
  * @see obi_close_dms()
  * @since May 2015
@@ -92,9 +92,8 @@ OBIDMS_p obi_create_dms(const char *dms_name);
  * @retval NULL on error and the `obi_errno`variable is set.
  *
  * ###Error values
- * 		- OBIDMS_EXIST_ERROR     : a database with the same name already exists.
  * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
- * 		- OBIDMS_MEMORY_ERROR    : something wrong occured during memory allocation.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
  *
  * @see obi_close_dms()
  * @since May 2015
@@ -118,7 +117,7 @@ OBIDMS_p obi_open_dms(const char *dms_name);
  *
  * ###Error values
  * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
- * 		- OBIDMS_MEMORY_ERROR    : something wrong occured during memory allocation.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
  *
  * @see obi_close_dms()
  * @since May 2015
diff --git a/src/obidmscolumn.c b/src/obidmscolumn.c
index 056a20c..164045c 100644
--- a/src/obidmscolumn.c
+++ b/src/obidmscolumn.c
@@ -1,5 +1,5 @@
 /****************************************************************************
- * OBIDMS_column functions                                                   *
+ * OBIDMS_column functions                                                  *
  ****************************************************************************/
 
 /**
@@ -13,22 +13,25 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <sys/types.h>
+#include <dirent.h>
 #include <unistd.h>
 #include <fcntl.h>
+#include <stdbool.h>
 #include <sys/mman.h>	/* mmap() is defined in this header */
 
 #include "obidmscolumn.h"
+#include "obidmscolumngroup.h"
 #include "obidms.h"
 #include "obitypes.h"
 #include "obierrno.h"
 #include "obilittlebigman.h"
-#include "private_openat.h"
+#include "private_at_functions.h"
 
-/*************************************************************************
+/**************************************************************************
  *
  * D E C L A R A T I O N   O F   T H E   P R I V A T E   F U N C T I O N S
  *
- *************************************************************************/
+ **************************************************************************/
 
 
 /**
@@ -44,7 +47,7 @@
  * @retvalue NULL if an error occurs
  *
  * ###Error values
- * 		- OBIDMS_MEMORY_ERROR    : something wrong occured during memory allocation.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
  *
  * @since May 2015
  * @author Eric Coissac (eric.coissac@metabarcoding.org)
@@ -90,7 +93,7 @@ static char *build_version_file_name(const char *column_name);
  * @since May 2015
  * @author Eric Coissac (eric.coissac@metabarcoding.org)
  */
-static obiversion_t obi_get_new_version_number(OBIDMS_p dms, char *column_name, bool block);
+static obiversion_t obi_get_new_version_number(OBIDMS_column_group_p column_group, bool block);
 
 
 /**
@@ -108,7 +111,7 @@ static obiversion_t obi_get_new_version_number(OBIDMS_p dms, char *column_name,
  * @since May 2015
  * @author Eric Coissac (eric.coissac@metabarcoding.org)
  */
-static int create_version_file(OBIDMS_p dms, char *column_name);
+static int create_version_file(OBIDMS_column_group_p column_group);
 
 
 /************************************************************************
@@ -124,7 +127,7 @@ static char *build_column_file_name(const char *column_name, obiversion_t versio
 	// Build the database directory name
 	if (asprintf(&filename,"%s@%d.odc", column_name, version_number) < 0)
 	{
-		obi_set_errno(OBIDMS_MEMORY_ERROR);
+		obi_set_errno(OBICOL_MEMORY_ERROR);
 		return NULL;
 	}
 
@@ -139,7 +142,7 @@ static char *build_version_file_name(const char *column_name)
 	// Build the database directory name
 	if (asprintf(&filename,"%s.odv", column_name) < 0)
 	{
-		obi_set_errno(OBIDMS_MEMORY_ERROR);
+		obi_set_errno(OBICOL_MEMORY_ERROR);
 		return NULL;
 	}
 
@@ -147,12 +150,12 @@ static char *build_version_file_name(const char *column_name)
 }
 
 
-static obiversion_t obi_get_new_version_number(OBIDMS_p dms, char *column_name, bool block)
+static obiversion_t obi_get_new_version_number(OBIDMS_column_group_p column_group, bool block)
 {
 	off_t 			loc_size;
 	obiversion_t 	new_version_number;
 	char* 			version_file_name;
-	int    			directory_file_descriptor;
+	int    			column_dir_file_descriptor;
 	int    			version_file_descriptor;
 	bool   			little_endian;
 	int 			lock_mode;
@@ -166,34 +169,31 @@ static obiversion_t obi_get_new_version_number(OBIDMS_p dms, char *column_name,
 	else
 		lock_mode=F_TLOCK;
 
-	// build the version file name
-	version_file_name = build_version_file_name(column_name);
+	// Build the version file name
+	version_file_name = build_version_file_name(column_group->column_name);
 	if (version_file_name == NULL)
 		return -1;
 
-	// Get the file descriptor associated to the database directory
-	directory_file_descriptor = dirfd(dms->directory);
-	if (directory_file_descriptor < 0)
+	// Get the file descriptor associated to the column group directory
+	column_dir_file_descriptor = dirfd(column_group->directory);
+	if (column_dir_file_descriptor < 0)
 	{
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
 		return -1;
 	}
 
-	//open the version file
-	version_file_descriptor = private_openat(directory_file_descriptor, version_file_name, O_RDWR);
-
+	// Open the version file
+	version_file_descriptor = private_openat(column_dir_file_descriptor, version_file_name, O_RDWR);
 	if (version_file_descriptor < 0)
 	{
 		free(version_file_name);
-
+		//close(column_dir_file_descriptor);
 		if (errno == ENOENT)
-		{
-			return create_version_file(dms, column_name);
-		}
+			return create_version_file(column_group);
 		else
 		{
-			obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+			obi_set_errno(OBICOL_UNKNOWN_ERROR);
 			return -1;
 		}
 	}
@@ -201,199 +201,223 @@ static obiversion_t obi_get_new_version_number(OBIDMS_p dms, char *column_name,
 	// Test if the version file size is ok
 	if (lseek(version_file_descriptor, 0, SEEK_END) < loc_size)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-	// prepare the file for locking
+	// Prepare the file for locking
 	if (lseek(version_file_descriptor, 0, SEEK_SET) != 0)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
 	// Lock the file
-	if (lockf(version_file_descriptor, lock_mode, loc_size) < -1)
+	if (lockf(version_file_descriptor, lock_mode, loc_size) < 0)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-	// read the endianess of the file
+	// Read the endianness of the file
     if (read(version_file_descriptor, &little_endian, sizeof(bool)) < sizeof(bool))
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-    // check if endianess is correct
+    // Check if endianness is correct
     if (little_endian != obi_is_little_endian())
 	{
+		obi_set_errno(OBICOL_BAD_ENDIAN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_BAD_ENDIAN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-    // read the current version number
+    // Read the current version number
     if (read(version_file_descriptor, &new_version_number, sizeof(obiversion_t)) < sizeof(obiversion_t))
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
     new_version_number++;
 
-    // write the new version number
+    // Write the new version number
 	if (lseek(version_file_descriptor, sizeof(bool), SEEK_SET) != sizeof(bool))
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
 	if (write(version_file_descriptor, &new_version_number, sizeof(obiversion_t)) < sizeof(obiversion_t))
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-	// prepare for the unlocking
+	// Prepare for unlocking
 	if (lseek(version_file_descriptor, 0, SEEK_SET) != 0)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-	// unlock the file
-	if (lockf(version_file_descriptor, F_ULOCK, loc_size) < -1)
+	// Unlock the file
+	if (lockf(version_file_descriptor, F_ULOCK, loc_size) < 0)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		close(column_dir_file_descriptor);
 		free(version_file_name);
 		return -1;
 	}
 
-	close(version_file_descriptor);
+	//close(version_file_descriptor);
+	//close(column_dir_file_descriptor);
 	free(version_file_name);
+
 	return new_version_number;
 }
 
 
-static int create_version_file(OBIDMS_p dms, char *column_name)
+static int create_version_file(OBIDMS_column_group_p column_group)
 {
 	off_t 			loc_size;
 	obiversion_t 	version_number;
 	char* 			version_file_name;
-	int    			directory_file_descriptor;
+	int    			column_dir_file_descriptor;
 	int    			version_file_descriptor;
 	bool   			little_endian;
 
 	loc_size = sizeof(bool) + sizeof(obiversion_t);
 	version_number = 0;
 
-	version_file_name = build_version_file_name(column_name);
-
+	version_file_name = build_version_file_name(column_group->column_name);
 	if (version_file_name == NULL)
 		return -1;
 
-	directory_file_descriptor = dirfd(dms->directory);
-	if (directory_file_descriptor < 0)
+	// Get the file descriptor associated to the column group directory
+	column_dir_file_descriptor = dirfd(column_group->directory);
+	if (column_dir_file_descriptor < 0)
 	{
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
 		return -1;
 	}
 
-	version_file_descriptor = private_openat(directory_file_descriptor,
-							  	  	  	  	 version_file_name,
-							  	  	  	  	 O_RDWR | O_CREAT);
-
+	// Get the file descriptor associated to the version file
+	version_file_descriptor = private_openat(column_dir_file_descriptor, version_file_name, O_RDWR | O_CREAT);
 	if (version_file_descriptor < 0)
 	{
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
 	// Lock the file
-	if (lockf(version_file_descriptor, F_LOCK, loc_size) < -1)
+	if (lockf(version_file_descriptor, F_LOCK, loc_size) < 0)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+	// Truncate the version file to the right size
 	if (ftruncate(version_file_descriptor, loc_size) < 0)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+	// Position offset to 0 to prepare for writing
 	if (lseek(version_file_descriptor, 0, SEEK_SET) != 0)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
 	little_endian = obi_is_little_endian();
 
+	// Write endianness
 	if (write(version_file_descriptor, &little_endian, sizeof(bool)) < sizeof(bool))
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+	// Write version number
 	if (write(version_file_descriptor, &version_number, sizeof(obiversion_t)) < sizeof(obiversion_t))
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
-	// prepare for the unlocking
+	// Prepare for unlocking
 	if (lseek(version_file_descriptor, 0, SEEK_SET) != 0)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
-	// unlock the file
-	if (lockf(version_file_descriptor, F_ULOCK, loc_size) < -1)
+	// Unlock the file
+	if (lockf(version_file_descriptor, F_ULOCK, loc_size) < 0)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
-	close(version_file_descriptor);
+	//close(version_file_descriptor);
+	//close(column_dir_file_descriptor);
 	free(version_file_name);
+
 	return version_number;
 }
 
@@ -404,80 +428,95 @@ static int create_version_file(OBIDMS_p dms, char *column_name)
  *
  **********************************************************************/
 
-obiversion_t obi_get_latest_version_number(OBIDMS_p dms, char *column_name)
+obiversion_t obi_get_latest_version_number(OBIDMS_column_group_p column_group)
 {
 	off_t 			loc_size;
 	obiversion_t 	latest_version_number;
 	char * 			version_file_name;
-	int    			directory_file_descriptor;
+	int    			column_dir_file_descriptor;
 	int    			version_file_descriptor;
 	bool   			little_endian;
 
 	loc_size = sizeof(bool) + sizeof(obiversion_t);
 	latest_version_number = 0;
 
-	version_file_name = build_version_file_name(column_name);
+	version_file_name = build_version_file_name(column_group->column_name);
 	if (version_file_name==NULL)
 		return -1;
 
-	directory_file_descriptor = dirfd(dms->directory);
-	if (directory_file_descriptor < 0) {
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+	// Get the file descriptor associated to the column group directory
+	column_dir_file_descriptor = dirfd(column_group->directory);
+	if (column_dir_file_descriptor < 0)
+	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
 		return -1;
 	}
 
-	version_file_descriptor = private_openat(directory_file_descriptor, version_file_name, O_RDONLY);
-
-	if (version_file_descriptor < 0) {
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+	// Get the file descriptor associated to the version file
+	version_file_descriptor = private_openat(column_dir_file_descriptor, version_file_name, O_RDONLY);
+	if (version_file_descriptor < 0)
+	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+	// Check that the version file size is ok
 	if (lseek(version_file_descriptor, 0, SEEK_END) < loc_size)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+	// Set the offset to 0 in the version file
 	if (lseek(version_file_descriptor, 0, SEEK_SET) != 0)
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+	// Read the endianness
     if (read(version_file_descriptor, &little_endian, sizeof(bool)) < sizeof(bool))
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+    // Verify the endianness
     if (little_endian != obi_is_little_endian())
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_BAD_ENDIAN_ERROR);
+		obi_set_errno(OBICOL_BAD_ENDIAN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
+    // Read the latest version number
     if (read(version_file_descriptor, &latest_version_number, sizeof(obiversion_t)) < sizeof(obiversion_t))
 	{
-		close(version_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		free(version_file_name);
+		close(version_file_descriptor);
+		close(column_dir_file_descriptor);
 		return -1;
 	}
 
-
-	close(version_file_descriptor);
 	free(version_file_name);
+	//close(version_file_descriptor);
+	//close(column_dir_file_descriptor);
+
 	return latest_version_number;
 }
 
@@ -489,104 +528,139 @@ size_t obi_get_platform_header_size()
 
 
 OBIDMS_column_p obi_create_column(OBIDMS_p dms,
-		                         char *column_name,
-								 OBIType_t type,
-								 size_t nb_elements)
+		                          const char *column_name,
+								  OBIType_t type,
+								  size_t nb_elements)
 {
 	OBIDMS_column_p 		new_column;
+	OBIDMS_column_group_p	column_group;
 	OBIDMS_column_header_p 	header;
 	size_t 					file_size;
 	obiversion_t 			version_number;
 	char* 					column_file_name;
 	int 					column_file_descriptor;
-	int 					directory_file_descriptor;
+	int						column_dir_file_descriptor;
 	size_t 					header_size;
 	size_t 					data_size;
 
 	new_column = NULL;
 
-	directory_file_descriptor = dirfd(dms->directory);
-	if (directory_file_descriptor < 0) {
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+	// Get the column group structure associated to the column
+	column_group = obi_column_group(dms, column_name);
+	if (column_group == NULL)
+		return NULL;
+
+	// Get the file descriptor associated to the column group directory
+	column_dir_file_descriptor = dirfd(column_group->directory);
+	if (column_dir_file_descriptor < 0)
+	{
+		obi_set_errno(OBICOLDIR_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
 		return NULL;
 	}
 
+	// Calculate the size needed
 	header_size = obi_get_platform_header_size();
 	data_size = obi_array_sizeof(type, nb_elements);
-
 	file_size = header_size + data_size;
 
-	version_number = obi_get_new_version_number(dms, column_name, true);
-
+	// Get the latest version number
+	version_number = obi_get_new_version_number(column_group, true);
 	if (version_number < 0)
 	{
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
 		return NULL;
 	}
 
+	// Get the column file name
 	column_file_name = build_column_file_name(column_name, version_number);
+	if (column_file_name == NULL)
+	{
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
+		return NULL;
+	}
 
-	column_file_descriptor =  private_openat(directory_file_descriptor,
-											 column_file_name,
-					   		   	   	   	   	 O_RDWR | O_CREAT);
+	// Open the column file
+	column_file_descriptor = private_openat(column_dir_file_descriptor, column_file_name, O_RDWR | O_CREAT);
+	if (column_file_descriptor < 0)
+	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
+		free(column_file_name);
+		return NULL;
+	}
 
+	// Truncate the column file to the right size
 	if (ftruncate(column_file_descriptor, file_size) < 0)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
 		close(column_file_descriptor);
-		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
 		free(column_file_name);
 		return NULL;
 	}
 
+	// Allocate the memory for the column structure
 	new_column = (OBIDMS_column_p) malloc(sizeof(OBIDMS_column_t));
-
-	if (new_column)
+	if (new_column == NULL)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
 		close(column_file_descriptor);
-		obi_set_errno(OBIDMS_MEMORY_ERROR);
 		free(column_file_name);
 		return NULL;
 	}
 
-	new_column->dms    = dms;
-	new_column->header = mmap(NULL,
-			                 header_size,
-					         PROT_READ | PROT_WRITE,
-					         MAP_SHARED,
-					         column_file_descriptor,
-					         0
-			                );
+	// Fill the column structure
+	new_column->dms    			 = dms;
+	new_column->column_group 	 = column_group;
+	new_column->header 			 = mmap(NULL,
+			                  	  	    header_size,
+			                  	  	    PROT_READ | PROT_WRITE,
+			                  	  	    MAP_SHARED,
+			                  	  	    column_file_descriptor,
+			                  	  	    0
+			                 	 	   );
 
 	if (new_column->header == MAP_FAILED)
 	{
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
 		close(column_file_descriptor);
-		obi_set_errno(OBIDMS_MEMORY_ERROR);
 		free(column_file_name);
 		free(new_column);
 		return NULL;
 	}
 
-	new_column->data   = mmap(NULL,
-			                 data_size,
-					         PROT_READ | PROT_WRITE,
-					         MAP_SHARED,
-					         column_file_descriptor,
-					         header_size
-			                );
+	new_column->data   			 = mmap(NULL,
+			                 	 	 	data_size,
+			                 	 	 	PROT_READ | PROT_WRITE,
+			                 	 	 	MAP_SHARED,
+			                 	 	 	column_file_descriptor,
+			                 	 	 	header_size
+			                			);
 
 	if (new_column->data == MAP_FAILED)
 	{
 		munmap(new_column->header, header_size);
+		obi_set_errno(OBICOL_UNKNOWN_ERROR);
+		obi_close_column_group(column_group);
+		close(column_dir_file_descriptor);
 		close(column_file_descriptor);
-		obi_set_errno(OBIDMS_MEMORY_ERROR);
 		free(column_file_name);
 		free(new_column);
 		return NULL;
 	}
 
-	new_column->writable= true;
+	new_column->writable  = true;
 
-	header = new_column->header;
+	header 				  = new_column->header;
 	header->little_endian = obi_is_little_endian();
 	header->header_size   = header_size;
 	header->line_count    = nb_elements;
@@ -598,14 +672,9 @@ OBIDMS_column_p obi_create_column(OBIDMS_p dms,
 	strncpy(header->name, column_name, OBIDMS_MAX_COLNAME);
 
 	free(column_file_name);
+	//obi_close_column_group(column_group);
+	//close(column_dir_file_descriptor);
+	//close(column_file_descriptor);
+
 	return new_column;
 }
-
-
-//	if( access( fname, F_OK ) != -1 ) {
-//	    // file exists
-//	} else {
-//	    // file doesn't exist
-//	}
-
-
diff --git a/src/obidmscolumn.h b/src/obidmscolumn.h
index ad2d3b4..a190175 100644
--- a/src/obidmscolumn.h
+++ b/src/obidmscolumn.h
@@ -22,11 +22,9 @@
 #include "obitypes.h"
 #include "obierrno.h"
 #include "obilittlebigman.h"
+#include "obidmscolumngroup.h"
 
 
-#define OBIDMS_MAX_COLNAME (128) /**< The maximum length of an OBIDMS column name
-                                  */
-
 typedef int32_t obiversion_t; 	/**< Used to store the column version number
                                  */
 
@@ -35,7 +33,7 @@ typedef int32_t obiversion_t; 	/**< Used to store the column version number
  */
 
 typedef struct OBIDMS_column_header {
-	bool			little_endian;		    /**< endianess of the column:
+	bool			little_endian;		    /**< endianness of the column:
 													- `true`  on little endian platforms
 													- `false` on big endian platforms
 
@@ -57,6 +55,7 @@ typedef struct OBIDMS_column_header {
 	 	 	 	 	 	 	 	 	 	 	 */
 } OBIDMS_column_header_t, *OBIDMS_column_header_p;
 
+
 /**
  * @brief Structure describing a Column of the OBITools DMS
  *
@@ -64,25 +63,27 @@ typedef struct OBIDMS_column_header {
  * creating, opening or cloning an OBIDMS_column.
  */
 typedef struct OBIDMS_column {
-	OBIDMS_p                dms   ; /**< A pointer to a DMS instance
-	                                 */
-	OBIDMS_column_header_p	header; /**< A pointer to the header of the column
-	                                 */
-	void*                   data;   /**< A `void` pointer to the beginning of the
-	                                 *   data.
-	                                 *
-	                                 *   @warning never use this member directly
-	                                 *            outside of the code of the
-	                                 *            low level functions
-	                                 *            of the OBITools DMS
-	                                 */
-	bool					writable;/**< Indicates if the column is writable or not.
-	                                  *       - `true` the column is writable
-	                                  *       - `false` the column is read-only
-	                                  *
-	                                  * A column is writable only by its creator
-	                                  * until it closes it.
-	                                  */
+	OBIDMS_p                dms;			 /**< A pointer to a DMS instance
+	                                 	 	  */
+	OBIDMS_column_group_p   column_group; 	 /**< A pointer to an OBIDMS column group instance
+	                                 	 	  */
+	OBIDMS_column_header_p	header; 		 /**< A pointer to the header of the column
+	                                 	 	  */
+	void*                   data;   		 /**< A `void` pointer to the beginning of the
+	                                 	 	  *   data.
+	                                 	 	  *
+	                                 	 	  *   @warning never use this member directly
+	                                 	 	  *            outside of the code of the
+	                                 	 	  *            low level functions
+	                                 	 	  *            of the OBITools DMS
+	                                 	 	  */
+	bool					writable;	     /**< Indicates if the column is writable or not.
+	                                  	  	  *       - `true` the column is writable
+	                                  	  	  *       - `false` the column is read-only
+	                                  	  	  *
+	                                  	  	  * A column is writable only by its creator
+	                                  	  	  * until it closes it.
+	                                  	  	  */
 } OBIDMS_column_t, *OBIDMS_column_p;
 
 
@@ -103,7 +104,7 @@ size_t obi_get_platform_header_size();
 /**
  * @brief Creates a column.
  *
- * @param dms a pointer as returned by obi_create_dms() or obi_open_dms()
+ * @param dms a pointer on an OBIDMS column
  * @param column_name the name of the new column
  * @param type the OBIType code used to create the column
  * @param nb_elements the number of elements to be stored
@@ -112,9 +113,9 @@ size_t obi_get_platform_header_size();
  * @author Eric Coissac (eric.coissac@metabarcoding.org)
  */
 OBIDMS_column_p obi_create_column(OBIDMS_p dms,
-								 char* column_name,
-								 OBIType_t type,
-								 size_t nb_elements);
+								  const char* column_name,
+								  OBIType_t type,
+								  size_t nb_elements);
 
 
 /**
@@ -126,7 +127,7 @@ OBIDMS_column_p obi_create_column(OBIDMS_p dms,
  * @return the bigger version number used for this column
  * @return -1 if the column does not exist
  */
-obiversion_t obi_get_latest_version_number(OBIDMS_p dms, char *column_name);
+obiversion_t obi_get_latest_version_number(OBIDMS_column_group_p column_group);
 
 
 #endif /* OBIDMSCOLUMN_H_ */
diff --git a/src/obidmscolumngroup.c b/src/obidmscolumngroup.c
new file mode 100644
index 0000000..cf8a28f
--- /dev/null
+++ b/src/obidmscolumngroup.c
@@ -0,0 +1,283 @@
+/****************************************************************************
+ * OBIDMS column groups functions                                      *
+ ****************************************************************************/
+
+/**
+ * @file obidmscolumngroup.c
+ * @author Celine Mercier
+ * @date 18 June 2015
+ * @brief Functions for OBIDMS column groups.
+ */
+
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "obidmscolumngroup.h"
+#include "obidms.h"
+#include "private_at_functions.h"
+#include "obierrno.h"
+
+
+/**************************************************************************
+ *
+ * D E C L A R A T I O N   O F   T H E   P R I V A T E   F U N C T I O N S
+ *
+ **************************************************************************/
+
+
+/**
+ * Internal function building the group directory name from an OBIDMS column name.
+ *
+ * The function builds the directory name corresponding to an OBIDMS column group.
+ * It checks also that the name is not too long.
+ *
+ * @warning The returned pointer has to be freed by the caller.
+ *
+ * @param column_name the name of the OBIDMS column
+ *
+ * @return a pointer to the OBIDMS column directory name
+ * @retvalue <column_directory_name> if everything is ok
+ * @retvalue NULL if an error occurs
+ *
+ * ###Error values
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
+ * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
+ *
+ * @since June 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+static char* build_column_directory_name(const char* column_name);
+
+
+/************************************************************************
+ *
+ * D E F I N I T I O N   O F   T H E   P R I V A T E   F U N C T I O N S
+ *
+ ************************************************************************/
+
+static char* build_column_directory_name(const char* column_name)
+{
+	char* column_directory_name;
+
+	// Build the database directory name
+	if (asprintf(&column_directory_name, "%s.obicol", column_name) < 0)
+	{
+		obi_set_errno(OBICOLDIR_MEMORY_ERROR);
+		return NULL;
+	}
+
+	// Test if the database name is not too long
+	if (strlen(column_directory_name) >= OBIDMS_COLUMN_DIR_MAX_NAME)
+	{
+		obi_set_errno(OBICOLDIR_LONG_NAME_ERROR);
+		free(column_directory_name);
+		return NULL;
+	}
+
+	return column_directory_name;
+}
+
+
+/**********************************************************************
+ *
+ * D E F I N I T I O N   O F   T H E   P U B L I C   F U N C T I O N S
+ *
+ **********************************************************************/
+
+int obi_column_group_exists(OBIDMS_p dms, const char* column_name)
+{
+    struct 	stat buffer;
+	char* 	column_directory_name;
+	char* 	full_path;
+    int 	check_dir;
+	int 	dms_file_descriptor;
+
+	// Build and check the directory name
+    column_directory_name = build_column_directory_name(column_name);
+	if (column_directory_name == NULL)
+	{
+		obi_set_errno(OBICOLDIR_UNKNOWN_ERROR);
+		return -1;
+	}
+
+	// Get the file descriptor for the dms
+	dms_file_descriptor = dirfd(dms->directory);
+	if (dms_file_descriptor < 0)
+	{
+		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		free(column_directory_name);
+		return -1;
+	}
+
+	// Get the full path for the column directory
+	full_path = get_full_path(dms_file_descriptor, column_directory_name);
+	if (full_path == NULL)
+	{
+		obi_set_errno(OBICOLDIR_UNKNOWN_ERROR);
+		free(column_directory_name);
+		return -1;
+	}
+
+	check_dir = stat(full_path, &buffer);
+
+	free(column_directory_name);
+	free(full_path);
+	//close(dms_file_descriptor);
+
+    if(check_dir == 0)
+        return 1;
+    else
+        return 0;
+}
+
+
+OBIDMS_column_group_p obi_create_column_group(OBIDMS_p dms, const char* column_name)
+{
+	char* 	column_directory_name;
+	int 	dms_file_descriptor;
+
+	// Build and check the directory name
+	column_directory_name = build_column_directory_name(column_name);
+	if (column_directory_name == NULL)
+	{
+		obi_set_errno(OBICOLDIR_UNKNOWN_ERROR);
+		return NULL;
+	}
+
+	// Get the file descriptor for the dms
+	dms_file_descriptor = dirfd(dms->directory);
+	if (dms_file_descriptor < 0)
+	{
+		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		free(column_directory_name);
+		return NULL;
+	}
+
+	// Try to create the directory
+	if (private_mkdirat(dms_file_descriptor, column_directory_name, 0x777) < 0)
+	{
+		if (errno == EEXIST)
+			obi_set_errno(OBICOLDIR_EXIST_ERROR);
+		else
+			obi_set_errno(OBICOLDIR_UNKNOWN_ERROR);
+		free(column_directory_name);
+		close(dms_file_descriptor);
+		return NULL;
+	}
+
+	free(column_directory_name);
+	//close(dms_file_descriptor);
+
+	return obi_open_column_group(dms, column_name);
+}
+
+
+OBIDMS_column_group_p obi_open_column_group(OBIDMS_p dms, const char* column_name)
+{
+	OBIDMS_column_group_p	column_group;
+	char*	 				column_directory_name;
+	DIR*					directory;
+	int 					dms_file_descriptor;
+
+	column_group = NULL;
+
+	// Build and check the directory name
+	column_directory_name = build_column_directory_name(column_name);
+	if (column_directory_name == NULL)
+		return NULL;
+
+	// Get the file descriptor for the dms
+	dms_file_descriptor = dirfd(dms->directory);
+	if (dms_file_descriptor < 0)
+	{
+		obi_set_errno(OBIDMS_UNKNOWN_ERROR);
+		free(column_directory_name);
+		return NULL;
+	}
+
+	// Try to open the column directory
+	directory = private_opendirat(dms_file_descriptor, column_directory_name);
+	if (directory == NULL) {
+		switch (errno)
+		{
+			case ENOENT:
+				obi_set_errno(OBICOLDIR_NOT_EXIST_ERROR);
+				break;
+
+			case EACCES:
+				obi_set_errno(OBICOLDIR_ACCESS_ERROR);
+				break;
+
+			case ENOMEM:
+				obi_set_errno(OBICOLDIR_MEMORY_ERROR);
+				break;
+
+			default:
+				obi_set_errno(OBICOLDIR_UNKNOWN_ERROR);
+		}
+		free(column_directory_name);
+		close(dms_file_descriptor);
+		return NULL;
+	}
+
+	// Allocate the column dir structure
+	column_group = (OBIDMS_column_group_p) malloc(sizeof(OBIDMS_column_group_t));
+	if (column_group == NULL)
+	{
+		obi_set_errno(OBICOLDIR_MEMORY_ERROR);
+		free(column_directory_name);
+		close(dms_file_descriptor);
+		return NULL;
+	}
+
+	// Initialize the data structure
+	strcpy(column_group->directory_name, column_directory_name);
+	strcpy(column_group->column_name, column_name);
+	column_group->directory = directory;
+
+	free(column_directory_name);
+	//close(dms_file_descriptor);
+
+	return column_group;
+}
+
+
+OBIDMS_column_group_p obi_column_group(OBIDMS_p dms, const char* column_name)
+{
+	int exists;
+	exists = obi_column_group_exists(dms, column_name);
+
+	switch (exists)
+	{
+		case 0:
+			return obi_create_column_group(dms, column_name);
+		case 1:
+			return obi_open_column_group(dms, column_name);
+	};
+
+	return NULL;
+}
+
+
+int obi_close_column_group(OBIDMS_column_group_p column_group)
+{
+	if (column_group != NULL)
+	{
+		// Close the column directory
+		if (closedir(column_group->directory) < 0)
+		{
+			obi_set_errno(OBICOLDIR_MEMORY_ERROR);
+			free(column_group);
+			return -1;
+		}
+		free(column_group);
+	}
+
+	return 0;
+}
+
diff --git a/src/obidmscolumngroup.h b/src/obidmscolumngroup.h
new file mode 100644
index 0000000..3176ceb
--- /dev/null
+++ b/src/obidmscolumngroup.h
@@ -0,0 +1,158 @@
+/****************************************************************************
+ * OBIDMS column directories header file                                    *
+ ****************************************************************************/
+
+/**
+ * @file obidmscolumngroup.h
+ * @author Celine Mercier
+ * @date 18 June 2015
+ * @brief Header file for OBIDMS column groups.
+ */
+
+#ifndef OBIDMSCOLUMNGROUP_H_
+#define OBIDMSCOLUMNGROUP_H_
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <dirent.h>
+
+#include "obidms.h"
+
+#define OBIDMS_MAX_COLNAME (128) /**< The maximum length of an OBIDMS column name
+                                  */
+
+#define OBIDMS_COLUMN_DIR_MAX_NAME (2048) 	/**< The maximum length of an OBIDMS column directory name
+                                		 */
+
+/** @brief A structure describing an OBIDMS column group instance
+ *
+ * A pointer to this structure is returned on creation
+ * and opening of an OBIDMS column group.
+ */
+
+typedef struct OBIDMS_column_group {
+	OBIDMS_p	dms;	 										/**< A pointer to a DMS instance.
+     	 	 	 	 	 	 	 	 	 	 	 	 		 	 */
+	char 		column_name[OBIDMS_MAX_COLNAME+1];				/**< The name of the column group
+																 *   contained in the directory.
+																 */
+	char		directory_name[OBIDMS_COLUMN_DIR_MAX_NAME+1];	/**< The name of the directory
+	                                     	 	 	 	 	 	 *   containing the column group.
+	                                     	 	 	 	 	 	 */
+	DIR*		directory;										/**< A directory entry usable to
+										 	 	 	 	 	 	 *   refer and scan the database directory.
+										 	 	 	 	 	 	 */
+} OBIDMS_column_group_t, *OBIDMS_column_group_p;
+
+
+/*@
+ * @brief Checks if an OBIDMS column group exists
+ *
+ * @param dms a pointer to an OBIDMS as returned by obi_create_dms() or obi_open_dms()
+ * @param column_name a pointer to a C string containing the name of the column.
+ *                    The actual directory name used to store the column is
+ *                    `<column_name>.obicol`.
+ *
+ * @return an integer value indicating the status of the column group
+ * @retvalue 1 the group exist
+ * @retvalue 0 the group does not exist
+ * @retvalue -1 an error occurred
+ *
+ * @see obi_close_column_group()
+ * @since June 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+int obi_column_group_exists(OBIDMS_p dms, const char* column_name);
+
+
+/**
+ * @brief Creates a new OBIDMS column group instance.
+ *
+ * A new OBIDMS column group is created. This function checks
+ * if a directory with this name does not already exist
+ * before creating the new column group.
+ *
+ * @param dms a pointer to an OBIDMS as returned by obi_create_dms() or obi_open_dms()
+ * @param column_name a pointer to a C string containing the name of the column.
+ *                    The actual directory name used to store the column will be
+ *                    `<column_name>.obicol`.
+ *
+ * @return a pointer to an OBIDMS column group structure describing the newly created
+ * 		   group
+ * @retval NULL on error and the `obi_errno` variable is set.
+ *
+ * ###Error values
+ * 		- OBIDMS_COL_DIR_EXIST_ERROR     : xxxxx a database with the same name already exists.
+ *
+ * @see obi_close_column_group()
+ * @since June 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+OBIDMS_column_group_p obi_create_column_group(OBIDMS_p dms, const char* column_name);
+
+
+/**
+ * @brief Opens an existing OBIDMS column group instance.
+ *
+ * @param dms a pointer to an OBIDMS as returned by obi_create_dms() or obi_open_dms()
+ * @param column_name a pointer to a C string containing the name of the column.
+ *                    The actual directory name used to store the column is
+ *                    `<column_name>.obicol`.
+ *
+ * @return a pointer to the OBIDMS column group structure describing the group
+ * @retval NULL on error and the `obi_errno`variable is set.
+ *
+ * ###Error values
+ * 		- OBIDMS_COL_DIR_ERROR     : xxxxx a database with the same name already exists.
+ *
+ * @see obi_close_column_group()
+ * @since June 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+OBIDMS_column_group_p obi_open_column_group(OBIDMS_p dms, const char* column_name);
+
+
+/**
+ * @brief Opens or creates a new OBIDMS column group instance.
+ *
+ * If the group already exists, this function opens it, otherwise it
+ * creates a new column group.
+ *
+ * @param dms a pointer to an OBIDMS as returned by obi_create_dms() or obi_open_dms()
+ * @param column_name a pointer to a C string containing the name of the column.
+ *                    The actual directory name used to store the column is
+ *                    `<column_name>.obicol`.
+ *
+ * @return a pointer to the OBIDMS column group structure describing the group
+ * @retval NULL on error and the `obi_errno`variable is set.
+ *
+ * ###Error values
+ * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurred during memory allocation.
+ *
+ * @since June 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+OBIDMS_column_group_p obi_column_group(OBIDMS_p dms, const char* column_name);
+
+
+/**
+ * @brief Closes an opened OBIDMS column group instance.
+ *
+ * @param column_group a pointer to an OBIDMS column group as returned by
+ * obi_create_column_group() or obi_open_column_group()
+ *
+ * @return an integer value indicating the success of the operation. Even on
+ * 		   error, the `OBIDMS_column_group` structure is freed
+ * @retvalue 0 on success
+ * @retvalue -1 on failure and the `obi_errno` variable is set.
+ *
+ * @see obi_create_column_group()
+ * @see obi_open_column_group()
+ * @since June 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+int obi_close_column_group(OBIDMS_column_group_p column_group);
+
+
+#endif /* OBIDMSCOLUMNDIR_H_ */
diff --git a/src/obitypes.c b/src/obitypes.c
index 2a8507f..ee6d8b1 100644
--- a/src/obitypes.c
+++ b/src/obitypes.c
@@ -8,7 +8,8 @@
 #include <obitypes.h>
 
 
-size_t obi_sizeof(OBIType_t type) {
+size_t obi_sizeof(OBIType_t type)
+{
 	size_t size=0;
 
 	switch (type) {
@@ -34,15 +35,16 @@ size_t obi_sizeof(OBIType_t type) {
 }
 
 
-size_t obi_array_sizeof(OBIType_t type, size_t nbelements) {
+size_t obi_array_sizeof(OBIType_t type, size_t nbelements)
+{
 	size_t size;
 	size_t rsize;
 	size_t psize;
 
 	size = obi_sizeof(type) * nbelements;
 
-	psize= getpagesize();
-	rsize= size % psize;
+	psize = getpagesize();
+	rsize = size % psize;
 
 	// Round at a size multiple of pagesize
 	if (rsize)