Map

Managing map objects in HDF5 (H5M)

The interface can only be used with the HDF5 VOL connectors that implement map objects. The native HDF5 library does not support this feature.

While the HDF5 data model is a flexible way to store data, some applications require a more general way to index information. HDF5 effectively uses key-value stores internally for a variety of purposes, but it does not expose a generic key-value store to the API. The Map APIs provide this capability to the HDF5 applications in the form of HDF5 map objects. These Map objects contain application-defined key-value stores, to which key-value pairs can be added, and from which values can be retrieved by key. 

HDF5 VOL connectors with support for map objects:

• DAOS

Example:

hid_t file_id, fapl_id, map_id, vls_type_id;
const char *names[2] = ["Alice", "Bob"];
uint64_t IDs[2] = [25385486, 34873275];
uint64_t val_out; 

<HDF5 VOL setup code ....> 
vls_type_id = H5Tcopy(H5T_C_S1); 
H5Tset_size(vls_type_id, H5T_VARIABLE); 
file_id = H5Fcreate("file.h5", H5F_ACC_TRUNC, H5P_DEFAULT, fapl_id); 
map_id = H5Mcreate(file_id, "map", vls_type_id, H5T_NATIVE_UINT64, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT); 
H5Mput(map_id, vls_type_id, &names[0], H5T_NATIVE_UINT64, &IDs[0], H5P_DEFAULT); 
H5Mput(map_id, vls_type_id, &names[1], H5T_NATIVE_UINT64, &IDs[1], H5P_DEFAULT); 
H5Mget(map_id, vls_type_id, &names[0], H5T_NATIVE_UINT64, &val_out, H5P_DEFAULT);
if(val_out != IDs[0]
   ERROR;
H5Mclose(map_id);
H5Tclose(vls_type_id);
H5Fclose(file_id);