Type system

Simple unified access to all data types

The datamodel API for accessing properties of an instance in SOFT5 has separate getters and setters for each type and number of dimensions. DLite generalizes and simplifies this by describing types and dimensionality of properties with 4 parameters:

• type: an enum defining the type of the data item (or items if it has dimensions). The table below summarises the implemented data types.

• size: the size of a data item in bytes.

• ndims: number of dimensions. Scalars has ndims=0.

• dims: array of length ndims with the length of each dimension. Note: in the future we will rename dims to shape. This change has already been implemented in the json parser/serialiser.

By taking these parameters as arguments, the functions dlite_datamodel_get_property() and dlite_datamodel_set_property() can handle all supported property types. No storage strategy is needed.

The table below summarises the different data types defined in DLite. More details, can be found in src/dlite-type.h. Also note that this supports arbitrary dimensional arrays. All arrays are assumed to be continuous in memory in C-order. DLite has currently no api for working with arrays as pointers to pointers.

type	datatype	sizes	description	examples
blob	dliteBlob	any	binary blob, sequence of bytes	blob32, blob128, …
bool	dliteBool	sizeof(bool)	boolean	bool
int	dliteInt	1, 2, 4, {8}	signed integer	(int), int8, int16, int32, {int64}
uint	dliteUInt	1, 2, 4, {8}	unsigned integer	(uint), uint8, uint16, uint32, {uint64}
float	dliteFloat	4, 8, {10, 12, 16}	floating point	(float), (double), float32, float64, {float80, float96, float128}
fixstring	dliteFixString	any	fix-sized NUL-terminated string	string20, string4000, …
ref	dliteRef	sizeof(DLiteInstance*)	reference to another instance	ref, http://onto-ns.com/meta/0.1/MyEntity
string	dliteStringPtr	sizeof(char *)	pointer to NUL-terminated string	string
relation	dliteRelation	sizeof(DLiteRelation)	subject-predicate-object triplet	relation
dimension	dliteDimension	sizeof(DLiteDimension)	only intended for metadata	dimension
property	dliteProperty	sizeof(DLiteProperty)	only intended for metadata	property

The examples shown in curly brackets may not be supported on all platforms. The size int, uint, float and double are platform-dependent. For portable applications you should provide the number of bits, like int32, uint32, float32, float64, etc… Note that the size specification of blob and fixstring are in bytes (not bits) and that the terminating NUL-character is included in the specified size of the fixstring types.