The lmt parameter file must in written in “eXtensible Markeup Language” (xml). For under-
standing the examples you may want to get a jump start in xml file structure first.
Don’t be scared. Even without any previous knowledge you’ll be able to understand the
xml structure used for lmt in less then half an hour. Please consult the Internet to find
suitable introduction into xml. Bare in mind that the lmt parameter file is case sensitive, that is
Hello is not the same as
Unsupported xml features
lmt's xml parsing capabilities are geared towards conveying information about linear mixed models, not to exchange information with other xml supporting software. Therefore, lmt only supports a particular set of xml features.
Parameter file terminology
The lmt parameter file has only two major structural components: elements and key strings. The content of each element can be one ore several other elements and one or several key strings.
An element starts at the start tag and ends at end tag and it's name is the character string between the arrow brackets of the tags. For example, the element name of <hello> is hello . Depending on the specific location and function of a element the name can be hard-coded or user-defined(u.d.). U.d. element names can be as short as possible. e.g. a single character, but must not contain any white space. While an element name my contain any ascii character it is strongly recommended to use only alpha-numeric characters and underscores.
Key strings have always the format keyword:variable . Keyword is a character string which is either hard coded or user defined. The spelling is therefore defined by the hardcoded value, or by the user, but must be abide by in any case. Variable refers to a
- a single character string, or comma-separated list of strings which may be hardcoded or user-defined, or
- a single or a comma-separated list of numeric values.
lmt parse the parameter file starting at the compulsory <root> element. Nested elements can be either automatic-compulsory , automatic-optional or nominated . Automatic-optional elements will be searched for by default and are evaluated if they are present. Their absence will not cause an error message at parsing time. However, that does not mean that the information they should provide is not necessary later on and it's absence may cause an error stop. Automatic-compulsory elements will be searched for by default and their absence will cause an error stop. Nominated elements are always compulsory but are only searched for if they have been nominated by a key string variable, where the key string variable becomes the element name.
Depending on the host element key strings can be optional or compulsory.
<root> <nest_1> </nest_1> <nest_2> <x> </x> others: y,z <y> </y> <z> </z> </nest_2> </root>
In the above example nested elements <nest_1> and <nest_2> maybe optional or compulsory, but both are automatic, that is lmt will evaluate them only if the are present. Element <x> , nested in element <nest_2> , is automatic and may be optional or compulsory as well. However, elements <y> and <z> are nominated and therefore compulsory. The nomination is triggered by providing key string other: y,z where the variable y,z provides a comma-separated list of names of the nominated elements. That is, after evaluating key string others: y,z lmt will search for elements <y> and <z> , and their absence will cause an error stop.
Note that non-sense and wrongly named key strings and elements will NOT cause an error stop as long as the parameter file content yields a sound description of the task and provides all necessary ingredients. Further, automatic-optional elements are evaluated even if they are not required for the task. This can lead to an unneccesary high demand for hard-ware resources and a substantially increased processing time. See here for an example.
Group of mutually exclusive information sources
For the sake of flexibility the user can supply the same information in several different ways to lmt. For instance, information can be embedded in an element or provided via a file where a key string variable contains the file name, e.g. file: filename . In such a case, the key string and the element form a Group of mutually exclusive information sources (GIS). The name already implies that lmt will accept only one source of information and if it finds more than one source will stop with an error message.
Escaping element content formatting rules
As pointed out above key strings are the only accept element content beside nested elements, and key strings must comply with a formatting rule. However, it is sometimes desirable to supply other information in an element where that information may not comply with the formatting rule. In order to do so the element content can be globally escaped by adding an attribute to the opening tag. However, this implies that by providing an attribute the whole element content is escaped, not just a single line.
<root> <nest_1 attribute="eligible_attribute"> you and me </nest_1> </root>
the content of nest_1 does not comply with the formatting rule keyword:variable as there is a colon missing. However, due to the attribute no error stop will occur.