Syntax Conventions

The following sections of this document describe the different operations that can be executed using VQL. The notation and syntax conventions used for this description are provided below.

  • The language is not case-sensitive. I.e. “CREATE VIEW” is equivalent to “create view”

  • The text in lower case and specified between the symbols “< and > (e.g. <name>) indicates an element whose specific syntax will be specified later. If the separator : appears (e.g. <name:element-definition>) | this indicates a name of a representative element followed by the name of the element that defines it.

  • The symbols ::= declare the definition of an element.

  • The square brackets ([]) indicate optional elements. When they must appear in a statement | they are specified in inverted commas to explicitly indicate that they should appear and that they do not indicate optional elements.

  • The asterisk (*) indicates that an element can be specified zero or more times. Example: [<search_method_clause>]* indicates that the element [<search_method_clause>] can be repeated as many times as necessary.

  • The plus sign (+) indicates that an element can be specified one or more times. Example: [<field>]+ indicates that the element [<field>] should appear at least once and can be repeated as many times as required.

  • Elements separated by the character | and possibly grouped between braces ({}) indicate alternative elements. For example: {element1 | element2} indicates that element1 or element2 have to be written in this position.

  • The commas (,) are used in syntax constructions to separate the elements of a list.

  • The brackets (()) normally serve to group expressions and increase priority. In some cases, they are required as part of the specific syntax of a statement.

  • The full stop (.) is used in numeric constants and to separate names of tables | columns and fields.

  • The whitespace character can be a space | a tab | a carriage return or a line jump.

  • Identifiers (<identifier>). Identifiers are the names of the elements of the catalog. If at least one of the characters of the identifier is not a number or in is not in the range of “a” to “z”, it is a <quoted identifier>. Therefore, | it has to be surrounded with double quotes ("). Certain words cannot be used as identifiers. See the definition of <reserved VQL words> in Basic primitives for specifying VQL statements.

  • Numbers (<number>). A number is a combination of digits that can be preceded by a - symbol and can include a full stop as a decimal separator point and optionally an exponent (if they are real numbers).

  • Logical values (<boolean>). Representation of the true and false logical values.

  • Literals (<literal>). They represent any string that is not an identifier nor a number nor a logical value. This may be any string that is found in inverted commas (single or double commas). If a literal contains single or double comma characters (depending on the case) | they should be escaped (\' and \" respectively).

  • Operators (<operator>). Represent operators in the system.

Basic primitives for specifying VQL statements
<identifier> ::=
    <basic identifier>
  | <quoted identifier>

<basic identifier> ::=
  [A-Za-z\200-\377][A-Za-z\200-\377_0-9\$]*

<quoted identifier> ::=
  ".*" (a double quote in an identifier has to be escaped with another double quote)

<view identifier> :: =
  <identifier with database>

<identifier with database> ::=
    <element name:identifier> (assumes that the element exists in the current database)
  | <database name:identifier>.<view name:identifier>

<integer> ::=
  [-][0-9]+

<number>  ::=
    <integer>
  | (([0-9]*\.[0-9]+)|([0-9]+\.[0-9]*)) ((([0-9]*\.[0-9]+)|([0-9]+\.[0-9]*)|([0-9]+))([Ee][-+][0-9]+))

<boolean> ::=
    TRUE
  | FALSE

<literal> ::= '.*' (a single quote in a literal has to be escaped with another single quote. E.g. 'literal''with a quote')

<operator> ::=
    <unary operator>
  | <binary operator>

<opsymbol> ::=
  [~!@#^&|?<>=]+

<unary operator> ::=
    is null
  | is not null
  | is true
  | is false

<binary operator> ::=
    =
  | <identifier>
  | <opsymbol>
  | IN

<reserved VQL words> ::=
    ADD | ALL | ALTER | AND | ANY | ARN | AS | ASC | BASE | BOTH | CALL
  | CASE | CONNECT | CONTEXT | CREATE | CROSS | CURRENT_DATE | CURRENT_TIMESTAMP
  | CUSTOM | DATABASE | DEFAULT | DESC | DF | DISTINCT | DROP | EXISTS | FALSE
  | FETCH | FLATTEN | FROM | FULL | GRANT | GROUP BY | GS | HASH | HAVING
  | HTML | IF | INNER | INTERSECT,INTO | IS | JDBC | JOIN | LDAP | LEADING
  | LEFT | LIMIT | MERGE | MINUS | MY | NATURAL | NESTED | NOS | NOT | NULL
  | OBL | ODBC | OF | OFF | OFFSET | ON | ONE | OPT | OR | ORDER BY | ORDERED
  | PRIVILEGES | READ | REVERSEORDER | REVOKE | RIGHT | ROW | SELECT | SWAP
  | TABLE | TO | TRACE | TRAILING | TRUE | UNION | USER | USING | VIEW | WHEN
  | WHERE | WITH | WRITE | WS | ZERO