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An ItemDef describes a type of item that can occur within a study. Item properties include name, datatype, measurement unitsrange, range or codelist restrictions, and several other properties.
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Note: The DataType attribute specifies how the allowable values and the intended use of the corresponding value elements are to be interpreted for comparison and storage. The Length attribute is required when DataType is text or string, optional when DataType is integer or float, and should not be given for the other datatypes. The SignificantDigits attribute is optional when DataType is float, and should not be given for the other datatypes. When DataType is float both Length and SignificantDigits must be given or both be absent, but not necessarily how systems will store them. The receiver is expected to preserve the value and precision of the data and can use the ODM-specified datatype to determine the best representation of the data in their system.
Note: In version 1ODM v1.3.0 2 the usage of Length and SignificantDigits was ambiguous. The above text clarifies the intention of these two attributes.
If DataType=integer, Length=N is a requirement that the receiving system be able to process and store all whole number values of magnitude less than 10N. Larger values may be rejected.
If DataType=float, Length=N and SignificantDigits=S is a requirement that the receiving system be able to process and store all numeric values of magnitude less than 10N-S that are multiples of 10-S. Larger values may be rejected. Intermediate values may be rounded to the nearest multiple of 10-S.
If DataType=text, Length=N is a requirement attributes were used to express the requirements for the receiving system. In ODM v2.0 the meaning of the Length attribute remains the same for the text and string datatypes, but has been changed for the numeric datatypes and is now optional for all datatypes. The SignificantDigits attribute has been removed. If DataType is text or a string and the Length attribute is provided, Length=N indicates that the receiving system be able to process and store all text string values of length less than or equal or equal to N. All characters are allowed are allowed in text string values. Data of type Text should be transmitted in an ItemDataString element.
When the Length attribute is provided, Length=N means that when a value of an item is represented as a text, its length must be less or equal to N. Length is a statement Note: Length and SignificantDigits are statements about an item's data s data values, not the number of characters used to represent these values in value in value elements. For example, the character "<<" might be represented as as "&lt;".
There are 3 datatypes available for floating-point values: decimal, float, and double. The decimal datatype represents a subset of the real numbers, which can be represented by decimal numerals. This datatype should be used for items with floating-point values when the number of decimal places is known in advance. For the decimal datatype, Length=N means that the number of characters required to represent the full numeric value, including the decimal character, must be less than or equal to N.
In cases where the number of decimal places is not known in advance or is not important, either float or double datatypes should be used. Both of these are patterned after the IEEE floating-point types. DataType=float corresponds to 4-byte single-precision floating-point type, with the basic value space consisting of the values m x 2e, where m is an integer whose absolute value is less than 224, and e is an integer between -149 and 104, inclusive. DataType=double corresponds to 8-byte double-precision floating-point type, with the basic value space consisting of the values m x 2e, where m is an integer whose absolute value is less than 253, and e is an integer between -1075 and 970, inclusive.
Note: Data Note: Data characters that are not included in the encoding character set for a particular ODM file must be represented using XML entities or character references. For example, Æ could be represented as "Æ".The SDSVarName, Origin, and Comment attributes carry submission information as described in the latest version of CDISC SDTM .
Note: In the ODM model, all internal keys are assumed to be unchangeable. This was done to make the audit trail issues work: if If the SubjectKey in the model were the actual external subject identifier (or randomization ID) of a patient, and that value is sent incorrectly in one ODM file, there would be no way to correct the mistake in a followup follow-up file. In doing this, we intend that the external subject keys (and other externally visible key variables) should be defined as Items in the metadata. Thus they can be modified through normal modify/audit mechanism. While Although this solves the problem of supporting modification of study keys, it leaves the user without a way to identify which ItemDefs have special meaning or what the meaning is. The most obvious place where this is a problem is in matching up patients when loading data from an external source. If you can't cannot find the patient ID, how do you do the matching? The answer is to use the SDSVarName attribute of ItemDef. SDSVarName is an optional attribute which create an Alias child element of ItemDef to provide an alternative name by, for example, setting with Context="SDSVarName" and Name="USUBJID". Setting Context to SDSVarName is a convention that can be used to tag the Item with a business meaning. Rather than try to enumerate all possible meanings in the ODM model, the ODM working group Data Exchange Standards Team thought it best to rely on the set of variable names defined in the CDISC SDTM, since ; this list covers the core variables used in managing clinical data. Software that is processing an ODM-compliant XML instance can therefore use specific values of the SDSVarName attribute Names when Context="SDSVarName" to identify standard, frequently used variables. The use of this attribute Context value is restricted to variables defined in the SDTM model. In tagging a variable, you are identifying it as matching the SDTM definition for that variable. A partial list of commonly used values includes:
See the SDTM Specification and Implementation Guide SDTMIG for more information about SDTM variables. |
The Question element contains the text shown to a human user when prompted to provide data for this Item. The ExternalQuestion element does the same but refers to an externally defined question. If both are present, they should be consistent.
The MeasurementUnitRefs list the acceptable measurement units for this type of item. Only numeric items can have measurement units. If only one MeasurementUnitRef is present, all items of this type carry this measurement unit by default, i.e. if a MeasurementUnitRef is defined on the ItemDef, and no MeasurementUnitRef is given on the corresponding ItemData, the value given by the ItemData has the units given by the ItemDef-MeasurementUnitRef.
If no MeasurementUnitRef is present on the definition of a numeric Item, the Item's value is scalar (i.e., a pure number).
The RangeChecks constrain the acceptable values for items of this type.
The CodeListRef (if present) constrains the acceptable values for items of this type to be members of the referenced codelist.
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