# Schema-Aware XQuery from the Command Line

To run a schema-aware query from the command line, use the `com.saxonica.Query` command instead of the usual `net.sf.saxon.Query`. This has an additional option `-val` to request validation of the source document. This applies not only to the principal source document loaded using the `-s` option on the command line, but to all documents loaded via the `doc()` functions, or supplied as additional command line parameters in the form `+param=doc.xml`.

As an alternative to the `-val` option, you can specify `-vlax` to request lax validation.

The schemas to be used to validate these source documents can be specified either by using the `import schema` declaration in the query prolog, or using `xsi:schemaLocation` (or `xsi:noNamespaceSchemaLocation`) attributes within the source documents themselves.

Validating the source document has several effects. Most obviously, it will cause the query to fail if the document is invalid. It will also cause default values for attributes and elements to be expanded, so they will appear to the query as if they were present on the source document. In addition, element and attribute nodes that have been validated will be annotated with a type. This enables operations to be performed in a type-safe way. This may cause error messages, for example if you try to use an xs:decimal value as an argument to a function that expects a string. It may also cause some operations to produce different results: for example when using elements or attributes that have been given a list type in the schema, the typed value of the node will appear in the stylesheet as a sequence rather than as a single string value.

The schema-aware version of Saxon also allows you to validate result documents (both final result documents and intermediate results). By default, elements constructed by the query are validated in lax mode, which means that they are validated if a schema declaration is available, and are not validated otherwise. You can set a different initial validation mode either using the `declare validation` declaration in the Query Prolog, or by issuing a call such as `staticQueryContext.pushValidationMode(Validation.SKIP)` in the calling API.

The `-vw` option on the command line causes validation errors encountered in processing a final result tree to be treated as warnings, allowing processing to continue. This allows more than one error to be reported in a single run. The result document is serialized as if validation were successful, but with XML comments inserted to show where the validation errors were found. This option does not necessarily recover from all validation errors, for example at present it does not recover from errors in uniqueness or referential constraints.

By default, the validation context for element constructors in the query depends on the textual nesting of the element constructors as written in the query. You can change the validation context (and the validation mode) if you need to, by using a `validate{}` expression within the query. For details of this expression, refer to the XQuery 1.0 specification. Validation of result documents is done on-the-fly, so if the query attempts to produce invalid output, you will usually get an error message that identifies the approximate location in the query where the error occurred.

The use of explicit and implicit validation contexts in XQuery is likely to change in the next version of the specification. However, Saxon currently implements something close to what is specified in the November 2003 draft.

With the schema-aware version of Saxon, declarations of functions and variables can refer to schema-defined types, for example you can write `let $a as schema-element(ipo:invoice)* := //inv`. You can also use the `element()` and `attribute()` tests to select nodes by their schema type in path expressions. See conformance.html to check which parts of the syntax have been implemented.

Saxon 8.2 does a certain amount of static analysis of the XQuery code based on schema information. For example, if a function argument is defined with a type such as `as="schema-element(invoice)"`, then it will check any path expressions used in the function body to ensure that they are valid against the schema when starting from `invoice` as the context node. Similarly, if the result type of a function is declared using an `as` attribute, then Saxon will check any direct element constructors in the body of the function to ensure that they are consistent with this declared type. This analysis can reveal many simple user errors at compile time that would otherwise result in run-time errors or simply in incorrect output. But this is only possible if the source code explicitly declares the types of variables and of function arguments and results.

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