SE Lon 9.39'35" SE Lat 20.49'21" Cloud coverage 63 % Receiving station Oberpfaffenhofen Channels 1, 2, 3, 4, 5 Address of archive DLR-DFD Of particular interest is the key attribute of a class. A key attribute contains a unique identifier for the objects of this class. This means that any two different objects have different values for this attribute. It is also possible to mark a sequence of attributes as the key attributes. In this case the concatenated values of these attributes form a unique identifier. Unique identifiers of objects can be used as values of other attributes to reference these objects. They are also used for some services (transfer, ordering) which require object identifiers as their input. In the example in Table 3-1 the attribute 'address_id' is the key attribute of the class 'address'. This means that values of these attributes are identifiers for objects of this class. These identifiers are used as the value of the attribute 'address of archive' to reference the archive addresses for the various images. Note that possible values for attributes are not only simple strings or numbers but also structured values (e.g., attribute 'region'), sets of values (e.g., attribute 'channels') or references to descriptions of other objects (e.g., attribute 'address of archive'). 3.2 Attribute Aspects Various characteristics can be associated with an attribute as part of the definition to help distinguish it from other attributes. These are termed 'attribute aspects'. The attribute aspects that can be specified for an attribute (apart from the attribute name) should include: Range (min/max): the valid (usually numeric) range for the attribute. Legal values: specifies the set of legal values for an attribute if applicable, (e.g., 'north-south', 'south-north'' for attribute 'direction of passage'). Description: short textual description of the attribute. Unit: the unit of the attribute (e.g., 'm', 'm/s' etc.). Default: a default value for the attribute (e.g., for a search result). Type: datatype, probably in software terms (e.g., 'int', 'string').
SE Lon 9.39'35" SE Lat 20.49'21" Cloud coverage 63 % Receiving station Oberpfaffenhofen Channels 1, 2, 3, 4, 5 Address of archive DLR-DFD Of particular interest is the key attribute of a class. A key attribute contains a unique identifier for the objects of this class. This means that any two different objects have different values for this attribute. It is also possible to mark a sequence of attributes as the key attributes. In this case the concatenated values of these attributes form a unique identifier. Unique identifiers of objects can be used as values of other attributes to reference these objects. They are also used for some services (transfer, ordering) which require object identifiers as their input. In the example in Table 3-1 the attribute 'address_id' is the key attribute of the class 'address'. This means that values of these attributes are identifiers for objects of this class. These identifiers are used as the value of the attribute 'address of archive' to reference the archive addresses for the various images. Note that possible values for attributes are not only simple strings or numbers but also structured values (e.g., attribute 'region'), sets of values (e.g., attribute 'channels') or references to descriptions of other objects (e.g., attribute 'address of archive'). 3.2 Attribute Aspects Various characteristics can be associated with an attribute as part of the definition to help distinguish it from other attributes. These are termed 'attribute aspects'. The attribute aspects that can be specified for an attribute (apart from the attribute name) should include: Range (min/max): the valid (usually numeric) range for the attribute. Legal values: specifies the set of legal values for an attribute if applicable, (e.g., 'north-south', 'south-north'' for attribute 'direction of passage'). Description: short textual description of the attribute. Unit: the unit of the attribute (e.g., 'm', 'm/s' etc.). Default: a default value for the attribute (e.g., for a search result). Type: datatype, probably in software terms (e.g., 'int', 'string').