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{-# LANGUAGE Arrows, RankNTypes, FlexibleContexts #-}
-- |An parser for the RDF/XML format
-- <http://www.w3.org/TR/REC-rdf-syntax/>.
module Text.RDF.RDF4H.XmlParser(
parseXmlRDF, getRDF
) where
import qualified Data.Map as Map
import Data.RDF
import Control.Arrow
import Text.XML.HXT.Core
import Data.ByteString.Lazy.Char8(ByteString)
import Data.String.Utils
-- |Global state for the parser
data GParseState = GParseState { stateGenId :: Int
}
-- |Local state for the parser (dependant on the parent xml elements)
data LParseState = LParseState { stateBaseUrl :: BaseUrl
, stateLang :: Maybe String
, stateSubject :: Subject
}
-- |Parse a xml ByteString to an RDF representation
parseXmlRDF :: forall rdf. (RDF rdf)
=> Maybe BaseUrl -- ^ The base URL for the RDF if required
-> Maybe ByteString -- ^ DocUrl: The request URL for the RDF if available
-> ByteString -- ^ The contents to parse
-> Either ParseFailure rdf -- ^ The RDF representation of the triples or ParseFailure
parseXmlRDF bUrl dUrl xmlStr = case runSLA (xread >>> addMetaData bUrl dUrl >>> getRDF) (GParseState { stateGenId = 0 }) (b2s xmlStr) of
(_,r:_) -> Right r
_ -> Left (ParseFailure "XML parsing failed")
-- |Add a root tag to a given XmlTree to appear as if it was read from a readDocument function
addMetaData :: (ArrowXml a) => Maybe BaseUrl -> Maybe ByteString -> a XmlTree XmlTree
addMetaData bUrlM dUrlM = mkelem "/"
( [ sattr "transfer-Message" "OK"
, sattr "transfer-MimeType" "text/rdf"
] ++ mkSource dUrlM ++ mkBase bUrlM
)
[ arr id ]
where mkSource (Just dUrl) = [ sattr "source" (b2s dUrl) ]
mkSource Nothing = []
mkBase (Just (BaseUrl bUrl)) = [ sattr "transfer-URI" (b2s bUrl) ]
mkBase Nothing = []
-- |Arrow that translates HXT XmlTree to an RDF representation
getRDF :: forall rdf a. (RDF rdf, ArrowXml a, ArrowState GParseState a) => a XmlTree rdf
getRDF = proc xml -> do
rdf <- hasName "rdf:RDF" <<< isElem <<< getChildren -< xml
bUrl <- arr (BaseUrl . s2b) <<< ((getAttrValue0 "xml:base" <<< isElem <<< getChildren) `orElse` getAttrValue "transfer-URI") -< xml
prefixMap <- arr toPrefixMap <<< toAttrMap -< rdf
triples <- parseDescription' >. id -< (bUrl, rdf)
returnA -< mkRdf triples (Just bUrl) prefixMap
where toAttrMap = (getAttrl >>> (getName &&& (getChildren >>> getText))) >. id
toPrefixMap = PrefixMappings . Map.fromList . map (\(n, m) -> (s2b (drop 6 n), s2b m)) . filter (startswith "xmlns:" . fst)
-- |Read the initial state from an rdf element
parseDescription' :: forall a. (ArrowXml a, ArrowState GParseState a) => a (BaseUrl, XmlTree) Triple
parseDescription' = proc (bUrl, rdf) -> do
desc <- isElem <<< getChildren -< rdf
state <- arr (\(s, o) -> s { stateSubject = o }) <<< arr fst &&& arr2A mkNode -< (LParseState bUrl Nothing undefined, desc)
triple <- parseDescription -< (state, desc)
returnA -< triple
-- |Read an rdf:Description tag to its corresponding Triples
parseDescription :: forall a. (ArrowXml a, ArrowState GParseState a) => a (LParseState, XmlTree) Triple
parseDescription = (updateState
>>> (arr2A parsePredicatesFromAttr
<+> (second (getChildren >>> isElem) >>> parsePredicatesFromChildren)
<+> (second (neg (hasName "rdf:Description")) >>> arr2A readTypeTriple))) -- If the rdf:Description element has another name, that is it's type
>>. (replaceLiElems [] (1 :: Int))
where readTypeTriple :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Triple
readTypeTriple state = getName >>> arr ((Triple (stateSubject state) ((unode . s2b) "rdf:type")) . unode . s2b)
replaceLiElems acc n (Triple s p o : rest) | p == (unode . s2b) "rdf:li" = replaceLiElems (Triple s ((unode . s2b) ("rdf:_" ++ show n)) o : acc) (n + 1) rest
replaceLiElems acc n (Triple s p o : rest) = replaceLiElems (Triple s p o : acc) n rest
replaceLiElems acc _ [] = acc
-- |Parse the current predicate element as a rdf:Description element (used when rdf:parseType = "Resource")
parseAsResource :: forall a. (ArrowXml a, ArrowState GParseState a) => Node -> a (LParseState, XmlTree) Triple
parseAsResource n = (updateState
>>> (arr2A parsePredicatesFromAttr
<+> (second getName >>> arr (\(s, p) -> Triple (stateSubject s) ((unode . s2b) p) n))
<+> (arr (\s -> s { stateSubject = n }) *** (getChildren >>> isElem) >>> parsePredicatesFromChildren))) -- If the rdf:Description element has another name, that is it's type
-- |Read the attributes of an rdf:Description element. These correspond to the Predicate Object pairs of the Triple
parsePredicatesFromAttr :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Triple
parsePredicatesFromAttr s = getAttrl >>> ((getName >>> neg (isMetaAttr)
>>> (arr (unode . s2b)))
&&& (getChildren >>> getText >>> arr (lnode . plainL . s2b))) >>> arr (attachSubject (stateSubject s))
isMetaAttr :: forall a. (ArrowXml a, ArrowState GParseState a) => a String String
isMetaAttr = isA (== "rdf:about")
<+> isA (== "rdf:nodeID")
<+> isA (== "rdf:ID")
<+> isA (== "xml:lang")
<+> isA (== "rdf:parseType")
-- |Read a children of an rdf:Description element. These correspond to the Predicate portion of the Triple
parsePredicatesFromChildren :: forall a. (ArrowXml a, ArrowState GParseState a) => a (LParseState, XmlTree) Triple
parsePredicatesFromChildren = updateState
>>> choiceA [ second (hasAttrValue "rdf:parseType" (== "Literal")) :-> arr2A parseAsLiteralTriple
, second (hasAttrValue "rdf:parseType" (== "Resource")) :-> (defaultA
<+> (mkBlankNode &&& arr id >>> arr2A parseAsResource))
, second (hasAttrValue "rdf:parseType" (== "Collection")) :-> (listA (defaultA >>> arr id &&& mkBlankNode) >>> mkCollectionTriples >>> unlistA)
, second (hasAttr "rdf:datatype") :-> arr2A getTypedTriple
, second (hasAttr "rdf:resource") :-> arr2A getResourceTriple
, second (hasAttr "rdf:nodeID") :-> arr2A getNodeIdTriple
, second (hasAttr "rdf:ID") :-> (arr2A mkRelativeNode &&& defaultA >>> arr2A reifyTriple >>> unlistA)
, this :-> (defaultA
<+> ((second getAttrl &&& (neg . second) (getAttrl >>> getName >>> isMetaAttr)) `guards` (mkBlankNode &&& arr id >>> arr2A parsePredicateAttr)))
]
where defaultA = proc (state, predXml) -> do
p <- arr(unode . s2b) <<< getName -< predXml
t <- arr2A (\s -> arr2A (parseObjectsFromChildren s)) <<< second (second getChildren) -< (state, (p, predXml))
returnA -< t
parsePredicateAttr n = (second getName >>> arr (\(s, p) -> Triple (stateSubject s) ((unode . s2b) p) n))
<+> (first (arr (\s -> s { stateSubject = n })) >>> arr2A parsePredicatesFromAttr)
parseObjectsFromChildren :: forall a. (ArrowXml a, ArrowState GParseState a)
=> LParseState -> Predicate -> a XmlTree Triple
parseObjectsFromChildren s p = (isText >>> getText >>> arr ((Triple (stateSubject s) p) . mkLiteralNode s))
<+> (isElem >>> hasName "rdf:Description" >>> parseObjectDescription) -- TODO: include ability to alias for rdf:type
where parseObjectDescription = proc desc -> do
o <- mkNode s -< desc
t0 <- arr (\(sub, (p, o)) -> Triple sub p o) -< (stateSubject s, (p, o))
t <- arr fst <+> (parseDescription <<< arr snd) -< (t0, (s { stateSubject = o }, desc))
returnA -< t
attachSubject :: Subject -> (Predicate, Object) -> Triple
attachSubject s (p, o) = Triple s p o
reifyTriple :: forall a. (ArrowXml a, ArrowState GParseState a) => Subject -> a Triple Triples
reifyTriple node = arr (\(Triple s p o) -> [ Triple s p o
, Triple node rdfType rdfStatement
, Triple node rdfSubject s
, Triple node rdfPredicate p
, Triple node rdfObject o
])
where rdfType = (unode . s2b) "rdf:type"
rdfStatement = (unode . s2b) "rdf:Statement"
rdfSubject = (unode . s2b) "rdf:subject"
rdfPredicate = (unode . s2b) "rdf:predicate"
rdfObject = (unode . s2b) "rdf:object"
-- |Updates the local state at a given node
updateState :: forall a. (ArrowXml a, ArrowState GParseState a)
=> a (LParseState, XmlTree) (LParseState, XmlTree)
updateState = (ifA (second (hasAttr "xml:lang")) (arr2A readLang) (arr id))
>>> (ifA (second (hasAttr "xml:base")) (arr2A readBase) (arr id))
where readLang state = (getAttrValue0 "xml:lang" >>> arr (\lang -> state { stateLang = Just lang } ) ) &&& arr id
readBase state = (getAttrValue0 "xml:base" >>> arr (\base -> state { stateBaseUrl = (BaseUrl . s2b) base } ) ) &&& arr id
-- |Read a Triple with an rdf:parseType of Literal
parseAsLiteralTriple :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Triple
parseAsLiteralTriple state = ((getName >>> arr (unode . s2b)) &&& (xshow ( getChildren ) >>> arr (mkTypedLiteralNode state nodeType))) >>> arr (attachSubject (stateSubject state))
where nodeType = mkFastString (s2b "http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral")
mkCollectionTriples :: forall a. (ArrowXml a, ArrowState GParseState a) => a [(Triple, Node)] Triples
mkCollectionTriples = arr (mkCollectionTriples' [])
where mkCollectionTriples' [] ((Triple s1 p1 o1, n1):rest) = mkCollectionTriples' [Triple s1 p1 n1] ((Triple s1 p1 o1, n1):rest)
mkCollectionTriples' acc ((Triple _ _ o1, n1):(t2, n2):rest) = mkCollectionTriples' (Triple n1 headNode o1 : Triple n1 tailNode n2 : acc) ((t2, n2):rest)
mkCollectionTriples' acc [(Triple _ _ o1, n1)] = Triple n1 headNode o1 : Triple n1 tailNode nilNode : acc
mkCollectionTriples' _ [] = []
headNode = (unode . s2b) "rdf:first"
tailNode = (unode . s2b) "rdf:rest"
nilNode = (unode . s2b) "rdf:nil"
-- |Read a Triple and it's type when rdf:datatype is available
getTypedTriple :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Triple
getTypedTriple state = ((getName >>> arr (unode . s2b)) &&& ((getAttrValue "rdf:datatype" &&& baseUrl >>> expandURI) &&& xshow (getChildren) >>> arr (\(t, v) -> lnode (typedL (s2b v) (mkFastString (s2b t)))))) >>> arr (attachSubject (stateSubject state))
where baseUrl = constA (case stateBaseUrl state of BaseUrl b -> b2s b)
getResourceTriple :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Triple
getResourceTriple state = ((getName >>> arr (unode . s2b)) &&& ((getAttrValue "rdf:resource" &&& baseUrl) >>> expandURI >>> arr (unode . s2b))) >>> arr (attachSubject (stateSubject state))
where baseUrl = constA (case stateBaseUrl state of BaseUrl b -> b2s b)
getNodeIdTriple :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Triple
getNodeIdTriple state = ((getName >>> arr (unode . s2b)) &&& (getAttrValue "rdf:nodeID" >>> arr (bnode . s2b))) >>> arr (attachSubject (stateSubject state))
-- |Read a Node from the "rdf:about" property or generate a blank node
mkNode :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Node
mkNode s = choiceA [ hasAttr "rdf:about" :-> (getAttrValue "rdf:about" &&& baseUrl >>> expandURI >>> arr (unode . s2b))
, hasAttr "rdf:resource" :-> (getAttrValue "rdf:resource" &&& baseUrl >>> expandURI >>> arr (unode . s2b))
, hasAttr "rdf:nodeID" :-> (getAttrValue "rdf:nodeID" >>> arr (bnode . s2b))
, hasAttr "rdf:ID" :-> mkRelativeNode s
, this :-> mkBlankNode
]
where baseUrl = constA (case stateBaseUrl s of BaseUrl b -> b2s b)
--mkRelativeNode :: forall a. (ArrowXml a, ArrowState GParseState a) => LParseState -> a XmlTree Node
mkRelativeNode s = (getAttrValue "rdf:ID" >>> arr (\x -> '#':x)) &&& baseUrl >>> expandURI >>> arr (unode . s2b)
where baseUrl = constA (case stateBaseUrl s of BaseUrl b -> b2s b)
mkTypedLiteralNode :: LParseState -> FastString -> String -> Node
mkTypedLiteralNode (LParseState _ _ _) t content = lnode (typedL (s2b content) t)
-- |Use the given state to create a literal node
mkLiteralNode :: LParseState -> String -> Node
mkLiteralNode (LParseState _ (Just lang) _) content = (lnode (plainLL (s2b content) (s2b lang)))
mkLiteralNode (LParseState _ Nothing _) content = (lnode . plainL . s2b) content
-- |Generate an RDF blank node with incrementing IDs from the arrow state
mkBlankNode :: forall a b. (ArrowState GParseState a) => a b Node
mkBlankNode = nextState (\gState -> gState { stateGenId = stateGenId gState + 1 } ) >>> arr (BNodeGen . stateGenId)
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