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6 Command file: Specifying the terms in the mixed model 84Choose labelsthat will avoidconfusion• data fields are identified in the model by their labels– labels are case sensitive,– labels may be abbreviated (truncated) when used in the model line but caremust be taken that the truncated form is not ambiguous. If the truncatedform matches more than one label, the term associated with the first matchis assumed,– model terms may only appear once in the model line; repeated occurrencesare ignored,– model terms other than the original data fields are defined the first time theyappear on the model line. They may be abbreviated (truncated) if they arereferred to again provided no ambiguity is introduced.Important It is often clearer if labels are not abbreviated. If abbreviationsare used then they need to be chosen to avoid confusion.• if the model is written over several lines, all but the final line must end with acomma to indicate that the list is continued.In Tables 6.1 and 6.2, the arguments in model term functions are represented bythe following symbolsf — the label of a data variable defined as a model factor,k, n — an integer number,r — a real number,t — a model term label (includes data variables),v, y — the label of a data variable,Parsing of model terms in ASReml is not very sophisticated. Where a model termtakes another model term as an argument, the argument must be predefined. Ifnecessary, include the argument in the model line with a leading ’-’ which willcause the term to be defined but not fitted. For exampleTrait.male -Trait.female and(Trait.female)Also, dens is an abbeviation for density but spl(dens,7) is a different modelterm (albiet probably equivalent) to spl(density,7) because it does not representa simple truncation.