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: querySrc ~ opt(loopExpression) ~ opt(selectClause) ~ opt(orderby) ~ opt(limitOffset)

querySrc: rep1sep(singleQrySrc, opt(COMMA))

singleQrySrc = FROM ~ fromSrc ~ opt(WHERE) ~ opt(expr ^? notIdExpression) |
        WHERE ~ (expr ^? notIdExpression) |
        expr ^? notIdExpression |
        fromSrc ~ opt(WHERE) ~ opt(expr ^? notIdExpression)

fromSrc: identifier ~ AS ~ alias | identifier

orderby: ORDERBY ~ expr ~ opt (sortOrder)
limitOffset: LIMIT ~ lmt ~ opt (offset)
offset: OFFSET ~ offsetValue 
sortOrder = ASC | DESC
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: {noformat} 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. {noformat}

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.atlas.query.ClosureQuery')
  • ORDERBY is optional. When order by clause is specified, case insensitive sorting is done based on the column specified.
For sorting in descending order specify 'DESC' after order by clause. If no order by is specified, then no default sorting is applied.
  • LIMIT is optional. It limits the maximum number of objects to be fetched starting from specified optional offset. If no offset is specified count starts from beginning.
  • There are couple of Predicate functions different from SQL:
    • is or isacan 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.
  • Any identifiers or constants with special characters(space,$,",{,}) should be enclosed within backquote (`)

DSL Examples

For the model, Asset - attributes name, owner, description DB - supertype Asset - attributes clusterName, parameters, comment Column - extends Asset - attributes type, comment Table - supertype Asset - db, columns, parameters, comment Traits - PII, Log Data

DSL queries: * from DB

  • DB where name="Reporting" select name, owner
  • DB where name="Reporting" select name, owner orderby name
  • DB where name="Reporting" select name limit 10
  • DB where name="Reporting" select name, owner limit 10 offset 0
  • DB where name="Reporting" select name, owner orderby name limit 10 offset 5
  • DB where name="Reporting" select name, owner orderby name desc limit 10 offset 5
  • 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
  • `Log Data`

Full-text Search

Atlas also exposes a lucene style full-text search capability.