diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index c0e5bc9b..69dba29e 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -11,7 +11,7 @@
 //! ```
 //! use rudf::model::*;
 //! use rudf::{Repository, RepositoryConnection, MemoryRepository, Result};
-//! use crate::rudf::sparql::PreparedQuery;
+//! use crate::rudf::sparql::{PreparedQuery, QueryOptions};
 //! use rudf::sparql::QueryResult;
 //!
 //! let repository = MemoryRepository::default();
@@ -27,7 +27,7 @@
 //! assert_eq!(vec![quad], results.unwrap());
 //!
 //! // SPARQL query
-//! let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", None).unwrap();
+//! let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", QueryOptions::default()).unwrap();
 //! let results = prepared_query.exec().unwrap();
 //! if let QueryResult::Bindings(results) = results {
 //!     assert_eq!(results.into_values_iter().next().unwrap().unwrap()[0], Some(ex.into()));
diff --git a/lib/src/repository.rs b/lib/src/repository.rs
index e1f9dde7..7d1aca4d 100644
--- a/lib/src/repository.rs
+++ b/lib/src/repository.rs
@@ -1,5 +1,5 @@
 use crate::model::*;
-use crate::sparql::PreparedQuery;
+use crate::sparql::{PreparedQuery, QueryOptions};
 use crate::{DatasetSyntax, GraphSyntax, Result};
 use std::io::BufRead;
 
@@ -14,7 +14,7 @@ use std::io::BufRead;
 /// ```
 /// use rudf::model::*;
 /// use rudf::{Repository, RepositoryConnection, MemoryRepository, Result};
-/// use crate::rudf::sparql::PreparedQuery;
+/// use crate::rudf::sparql::{PreparedQuery, QueryOptions};
 /// use rudf::sparql::QueryResult;
 ///
 /// let repository = MemoryRepository::default();
@@ -30,7 +30,7 @@ use std::io::BufRead;
 /// assert_eq!(vec![quad], results.unwrap());
 ///
 /// // SPARQL query
-/// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", None).unwrap();
+/// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", QueryOptions::default()).unwrap();
 /// let results = prepared_query.exec().unwrap();
 /// if let QueryResult::Bindings(results) = results {
 ///     assert_eq!(results.into_values_iter().next().unwrap().unwrap()[0], Some(ex.into()));
@@ -64,7 +64,7 @@ pub trait RepositoryConnection: Clone {
     /// ```
     /// use rudf::model::*;
     /// use rudf::{Repository, RepositoryConnection, MemoryRepository};
-    /// use rudf::sparql::PreparedQuery;
+    /// use rudf::sparql::{PreparedQuery, QueryOptions};
     /// use rudf::sparql::QueryResult;
     ///
     /// let repository = MemoryRepository::default();
@@ -75,13 +75,13 @@ pub trait RepositoryConnection: Clone {
     /// connection.insert(&Quad::new(ex.clone(), ex.clone(), ex.clone(), None));
     ///
     /// // SPARQL query
-    /// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", None).unwrap();
+    /// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", QueryOptions::default()).unwrap();
     /// let results = prepared_query.exec().unwrap();
     /// if let QueryResult::Bindings(results) = results {
     ///     assert_eq!(results.into_values_iter().next().unwrap().unwrap()[0], Some(ex.into()));
     /// }
     /// ```
-    fn prepare_query(&self, query: &str, base_iri: Option<&str>) -> Result<Self::PreparedQuery>;
+    fn prepare_query(&self, query: &str, options: QueryOptions) -> Result<Self::PreparedQuery>;
 
     /// Retrieves quads with a filter on each quad component
     ///
diff --git a/lib/src/sparql/mod.rs b/lib/src/sparql/mod.rs
index a48a4244..dbbbdb6c 100644
--- a/lib/src/sparql/mod.rs
+++ b/lib/src/sparql/mod.rs
@@ -31,9 +31,9 @@ pub trait PreparedQuery {
 }
 
 /// An implementation of `PreparedQuery` for internal use
-pub struct SimplePreparedQuery<S: StoreConnection>(SimplePreparedQueryOptions<S>);
+pub struct SimplePreparedQuery<S: StoreConnection>(SimplePreparedQueryAction<S>);
 
-enum SimplePreparedQueryOptions<S: StoreConnection> {
+enum SimplePreparedQueryAction<S: StoreConnection> {
     Select {
         plan: PlanNode,
         variables: Vec<Variable>,
@@ -55,17 +55,17 @@ enum SimplePreparedQueryOptions<S: StoreConnection> {
 }
 
 impl<S: StoreConnection> SimplePreparedQuery<S> {
-    pub(crate) fn new(connection: S, query: &str, base_iri: Option<&str>) -> Result<Self> {
-        let dataset = DatasetView::new(connection);
+    pub(crate) fn new(connection: S, query: &str, options: QueryOptions) -> Result<Self> {
+        let dataset = DatasetView::new(connection, options.default_graph_as_union);
         //TODO avoid inserting terms in the Repository StringStore
-        Ok(Self(match read_sparql_query(query, base_iri)? {
+        Ok(Self(match read_sparql_query(query, options.base_iri)? {
             QueryVariants::Select {
                 algebra,
                 dataset: _,
                 base_iri,
             } => {
                 let (plan, variables) = PlanBuilder::build(dataset.encoder(), &algebra)?;
-                SimplePreparedQueryOptions::Select {
+                SimplePreparedQueryAction::Select {
                     plan,
                     variables,
                     evaluator: SimpleEvaluator::new(dataset, base_iri),
@@ -77,7 +77,7 @@ impl<S: StoreConnection> SimplePreparedQuery<S> {
                 base_iri,
             } => {
                 let (plan, _) = PlanBuilder::build(dataset.encoder(), &algebra)?;
-                SimplePreparedQueryOptions::Ask {
+                SimplePreparedQueryAction::Ask {
                     plan,
                     evaluator: SimpleEvaluator::new(dataset, base_iri),
                 }
@@ -89,7 +89,7 @@ impl<S: StoreConnection> SimplePreparedQuery<S> {
                 base_iri,
             } => {
                 let (plan, variables) = PlanBuilder::build(dataset.encoder(), &algebra)?;
-                SimplePreparedQueryOptions::Construct {
+                SimplePreparedQueryAction::Construct {
                     plan,
                     construct: PlanBuilder::build_graph_template(
                         dataset.encoder(),
@@ -105,7 +105,7 @@ impl<S: StoreConnection> SimplePreparedQuery<S> {
                 base_iri,
             } => {
                 let (plan, _) = PlanBuilder::build(dataset.encoder(), &algebra)?;
-                SimplePreparedQueryOptions::Describe {
+                SimplePreparedQueryAction::Describe {
                     plan,
                     evaluator: SimpleEvaluator::new(dataset, base_iri),
                 }
@@ -117,26 +117,55 @@ impl<S: StoreConnection> SimplePreparedQuery<S> {
 impl<S: StoreConnection> PreparedQuery for SimplePreparedQuery<S> {
     fn exec(&self) -> Result<QueryResult<'_>> {
         match &self.0 {
-            SimplePreparedQueryOptions::Select {
+            SimplePreparedQueryAction::Select {
                 plan,
                 variables,
                 evaluator,
             } => evaluator.evaluate_select_plan(&plan, &variables),
-            SimplePreparedQueryOptions::Ask { plan, evaluator } => {
+            SimplePreparedQueryAction::Ask { plan, evaluator } => {
                 evaluator.evaluate_ask_plan(&plan)
             }
-            SimplePreparedQueryOptions::Construct {
+            SimplePreparedQueryAction::Construct {
                 plan,
                 construct,
                 evaluator,
             } => evaluator.evaluate_construct_plan(&plan, &construct),
-            SimplePreparedQueryOptions::Describe { plan, evaluator } => {
+            SimplePreparedQueryAction::Describe { plan, evaluator } => {
                 evaluator.evaluate_describe_plan(&plan)
             }
         }
     }
 }
 
+/// Options for SPARQL query parsing and evaluation like the query base IRI
+pub struct QueryOptions<'a> {
+    pub(crate) base_iri: Option<&'a str>,
+    pub(crate) default_graph_as_union: bool,
+}
+
+impl<'a> Default for QueryOptions<'a> {
+    fn default() -> Self {
+        Self {
+            base_iri: None,
+            default_graph_as_union: false,
+        }
+    }
+}
+
+impl<'a> QueryOptions<'a> {
+    /// Allows to set the base IRI of the query
+    pub fn with_base_iri(mut self, base_iri: &'a str) -> Self {
+        self.base_iri = Some(base_iri);
+        self
+    }
+
+    /// Consider the union of all graphs in the repository as the default graph
+    pub fn with_default_graph_as_union(mut self) -> Self {
+        self.default_graph_as_union = true;
+        self
+    }
+}
+
 /// A parsed [SPARQL query](https://www.w3.org/TR/sparql11-query/)
 #[derive(Eq, PartialEq, Debug, Clone, Hash)]
 pub struct Query(QueryVariants);
diff --git a/lib/src/sparql/plan.rs b/lib/src/sparql/plan.rs
index 370746f1..88d1a912 100644
--- a/lib/src/sparql/plan.rs
+++ b/lib/src/sparql/plan.rs
@@ -1,6 +1,7 @@
 use crate::sparql::eval::StringOrStoreString;
 use crate::store::numeric_encoder::{
     EncodedQuad, EncodedTerm, Encoder, MemoryStrStore, StrContainer, StrLookup,
+    ENCODED_DEFAULT_GRAPH,
 };
 use crate::store::StoreConnection;
 use crate::Result;
@@ -462,13 +463,15 @@ pub enum TripleTemplateValue {
 pub struct DatasetView<S: StoreConnection> {
     store: S,
     extra: RefCell<MemoryStrStore>,
+    default_graph_as_union: bool,
 }
 
 impl<S: StoreConnection> DatasetView<S> {
-    pub fn new(store: S) -> Self {
+    pub fn new(store: S, default_graph_as_union: bool) -> Self {
         Self {
             store,
             extra: RefCell::new(MemoryStrStore::default()),
+            default_graph_as_union,
         }
     }
 
@@ -479,8 +482,33 @@ impl<S: StoreConnection> DatasetView<S> {
         object: Option<EncodedTerm>,
         graph_name: Option<EncodedTerm>,
     ) -> Box<dyn Iterator<Item = Result<EncodedQuad>> + 'a> {
-        self.store
-            .quads_for_pattern(subject, predicate, object, graph_name)
+        if graph_name == None {
+            Box::new(
+                self.store
+                    .quads_for_pattern(subject, predicate, object, None)
+                    .filter(|quad| match quad {
+                        Err(_) => true,
+                        Ok(quad) => quad.graph_name != ENCODED_DEFAULT_GRAPH,
+                    }),
+            )
+        } else if graph_name == Some(ENCODED_DEFAULT_GRAPH) && self.default_graph_as_union {
+            Box::new(
+                self.store
+                    .quads_for_pattern(subject, predicate, object, None)
+                    .map(|quad| {
+                        let quad = quad?;
+                        Ok(EncodedQuad::new(
+                            quad.subject,
+                            quad.predicate,
+                            quad.object,
+                            ENCODED_DEFAULT_GRAPH,
+                        ))
+                    }),
+            )
+        } else {
+            self.store
+                .quads_for_pattern(subject, predicate, object, graph_name)
+        }
     }
 
     pub fn encoder<'a>(&'a self) -> impl Encoder + StrContainer + 'a {
diff --git a/lib/src/store/memory.rs b/lib/src/store/memory.rs
index b0aaecb2..d9cbe5cd 100644
--- a/lib/src/store/memory.rs
+++ b/lib/src/store/memory.rs
@@ -14,7 +14,7 @@ use std::sync::{PoisonError, RwLock, RwLockReadGuard, RwLockWriteGuard};
 /// use rudf::model::*;
 /// use rudf::{Repository, RepositoryConnection, MemoryRepository, Result};
 /// use crate::rudf::sparql::PreparedQuery;
-/// use rudf::sparql::QueryResult;
+/// use rudf::sparql::{QueryResult, QueryOptions};
 ///
 /// let repository = MemoryRepository::default();
 /// let mut connection = repository.connection().unwrap();
@@ -29,7 +29,7 @@ use std::sync::{PoisonError, RwLock, RwLockReadGuard, RwLockWriteGuard};
 /// assert_eq!(vec![quad], results.unwrap());
 ///
 /// // SPARQL query
-/// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", None).unwrap();
+/// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", QueryOptions::default()).unwrap();
 /// let results = prepared_query.exec().unwrap();
 /// if let QueryResult::Bindings(results) = results {
 ///     assert_eq!(results.into_values_iter().next().unwrap().unwrap()[0], Some(ex.into()));
diff --git a/lib/src/store/mod.rs b/lib/src/store/mod.rs
index 7b1a0260..e648a824 100644
--- a/lib/src/store/mod.rs
+++ b/lib/src/store/mod.rs
@@ -10,7 +10,7 @@ pub use crate::store::memory::MemoryRepository;
 pub use crate::store::rocksdb::RocksDbRepository;
 
 use crate::model::*;
-use crate::sparql::SimplePreparedQuery;
+use crate::sparql::{QueryOptions, SimplePreparedQuery};
 use crate::store::numeric_encoder::*;
 use crate::{DatasetSyntax, GraphSyntax, RepositoryConnection, Result};
 use rio_api::parser::{QuadsParser, TriplesParser};
@@ -71,8 +71,8 @@ impl<S: StoreConnection> From<S> for StoreRepositoryConnection<S> {
 impl<S: StoreConnection> RepositoryConnection for StoreRepositoryConnection<S> {
     type PreparedQuery = SimplePreparedQuery<S>;
 
-    fn prepare_query(&self, query: &str, base_iri: Option<&str>) -> Result<SimplePreparedQuery<S>> {
-        SimplePreparedQuery::new(self.inner.clone(), query, base_iri) //TODO: avoid clone
+    fn prepare_query(&self, query: &str, options: QueryOptions) -> Result<SimplePreparedQuery<S>> {
+        SimplePreparedQuery::new(self.inner.clone(), query, options) //TODO: avoid clone
     }
 
     fn quads_for_pattern<'a>(
diff --git a/lib/src/store/rocksdb.rs b/lib/src/store/rocksdb.rs
index cb0b79de..416855bf 100644
--- a/lib/src/store/rocksdb.rs
+++ b/lib/src/store/rocksdb.rs
@@ -24,7 +24,7 @@ use std::str;
 /// ```ignored
 /// use rudf::model::*;
 /// use rudf::{Repository, RepositoryConnection, RocksDbRepository, Result};
-/// use crate::rudf::sparql::PreparedQuery;
+/// use crate::rudf::sparql::{PreparedQuery, QueryOptions};
 /// use rudf::sparql::QueryResult;
 ///
 /// let repository = RocksDbRepository::open("example.db").unwrap();
@@ -40,7 +40,7 @@ use std::str;
 /// assert_eq!(vec![quad], results.unwrap());
 ///
 /// // SPARQL query
-/// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", None).unwrap();
+/// let prepared_query = connection.prepare_query("SELECT ?s WHERE { ?s ?p ?o }", QueryOptions::default()).unwrap();
 /// let results = prepared_query.exec().unwrap();
 /// if let QueryResult::Bindings(results) = results {
 ///     assert_eq!(results.into_values_iter().next().unwrap().unwrap()[0], Some(ex.into()));
diff --git a/lib/tests/sparql_test_cases.rs b/lib/tests/sparql_test_cases.rs
index f76dec9d..fcef66c3 100644
--- a/lib/tests/sparql_test_cases.rs
+++ b/lib/tests/sparql_test_cases.rs
@@ -4,7 +4,7 @@ use rayon::prelude::*;
 use rudf::model::vocab::rdf;
 use rudf::model::vocab::rdfs;
 use rudf::model::*;
-use rudf::sparql::PreparedQuery;
+use rudf::sparql::{PreparedQuery, QueryOptions};
 use rudf::sparql::{Query, QueryResult, QueryResultSyntax};
 use rudf::{GraphSyntax, MemoryRepository, Repository, RepositoryConnection, Result};
 use std::fmt;
@@ -158,7 +158,7 @@ fn sparql_w3c_query_evaluation_testsuite() -> Result<()> {
             }
             match repository
                 .connection()?
-                .prepare_query(&read_file_to_string(&test.query)?, Some(&test.query))
+                .prepare_query(&read_file_to_string(&test.query)?, QueryOptions::default().with_base_iri(&test.query))
             {
                 Err(error) => Err(format_err!(
                     "Failure to parse query of {} with error: {}",
diff --git a/server/src/main.rs b/server/src/main.rs
index da7bcea6..3c2cd587 100644
--- a/server/src/main.rs
+++ b/server/src/main.rs
@@ -4,8 +4,7 @@ use clap::ArgMatches;
 use rouille::input::priority_header_preferred;
 use rouille::url::form_urlencoded;
 use rouille::{content_encoding, start_server, Request, Response};
-use rudf::sparql::QueryResult;
-use rudf::sparql::{PreparedQuery, QueryResultSyntax};
+use rudf::sparql::{PreparedQuery, QueryOptions, QueryResult, QueryResultSyntax};
 use rudf::{
     DatasetSyntax, FileSyntax, GraphSyntax, MemoryRepository, Repository, RepositoryConnection,
     RocksDbRepository,
@@ -149,7 +148,7 @@ fn evaluate_sparql_query<R: RepositoryConnection>(
     request: &Request,
 ) -> Response {
     //TODO: stream
-    match connection.prepare_query(query, None) {
+    match connection.prepare_query(query, QueryOptions::default()) {
         Ok(query) => {
             let results = query.exec().unwrap();
             if let QueryResult::Graph(_) = results {