blob: 7e7be28d9aa73e2ac6b40d753bbbdebcd8805b52 [file] [log] [blame]
---+ Search
Atlas exposes search over the metadata in two ways:
* Search using DSL
* Full-text search
---++ Search DSL Grammar
The DSL exposes an SQL like query language for searching the metadata based on the type system.
The grammar for the DSL is below.
queryWithPath: query ~ opt(WITHPATH)
query: rep1sep(singleQuery, opt(COMMA))
singleQuery: singleQrySrc ~ opt(loopExpression) ~ opt(selectClause)
singleQrySrc = FROM ~ fromSrc ~ opt(WHERE) ~ opt(expr ^? notIdExpression) |
WHERE ~ (expr ^? notIdExpression) |
expr ^? notIdExpression |
fromSrc ~ opt(WHERE) ~ opt(expr ^? notIdExpression)
fromSrc: identifier ~ AS ~ alias | identifier
loopExpression: LOOP ~ (LPAREN ~> query <~ RPAREN) ~ opt(intConstant <~ TIMES) ~ opt(AS ~> alias)
selectClause: SELECT ~ rep1sep(selectExpression, COMMA)
selectExpression: expr ~ opt(AS ~> alias)
expr: compE ~ opt(rep(exprRight))
exprRight: (AND | OR) ~ compE
arithE ~ (LT | LTE | EQ | NEQ | GT | GTE) ~ arithE |
arithE ~ (ISA | IS) ~ ident |
arithE ~ HAS ~ ident |
arithE: multiE ~ opt(rep(arithERight))
arithERight: (PLUS | MINUS) ~ multiE
multiE: atomE ~ opt(rep(multiERight))
multiERight: (STAR | DIV) ~ atomE
atomE: literal | identifier | LPAREN ~> expr <~ RPAREN
identifier: rep1sep(ident, DOT)
alias: ident | stringLit
literal: booleanConstant |
intConstant |
longConstant |
floatConstant |
doubleConstant |
Grammar language:
opt(a) => a is optional
~ => a combinator. 'a ~ b' means a followed by b
rep => zero or more
rep1sep => one or more, separated by second arg.
Language Notes:
* A *SingleQuery* expression can be used to search for entities of a _Trait_ or _Class_.
Entities can be filtered based on a 'Where Clause' and Entity Attributes can be retrieved based on a 'Select Clause'.
* An Entity Graph can be traversed/joined by combining one or more SingleQueries.
* An attempt is made to make the expressions look SQL like by accepting keywords "SELECT",
"FROM", and "WHERE"; but these are optional and users can simply think in terms of Entity Graph Traversals.
* The transitive closure of an Entity relationship can be expressed via the _Loop_ expression. A
_Loop_ expression can be any traversal (recursively a query) that represents a _Path_ that ends in an Entity of the same _Type_ as the starting Entity.
* The _WithPath_ clause can be used with transitive closure queries to retrieve the Path that
connects the two related Entities. (We also provide a higher level interface for Closure Queries see scaladoc for 'org.apache.metadata.query.ClosureQuery')
* There are couple of Predicate functions different from SQL:
* _is_ or _isa_can be used to filter Entities that have a particular Trait.
* _has_ can be used to filter Entities that have a value for a particular Attribute.
---+++ DSL Examples
* from DB
* DB where name="Reporting" select name, owner
* DB has name
* DB is JdbcAccess
* Column where Column isa PII
* Table where name="sales_fact", columns
* Table where name="sales_fact", columns as column select, column.dataType, column.comment
---++ Full-text Search
Atlas also exposes a lucene style full-text search capability.