diff --git a/contracts/okp4-cognitarium/src/contract.rs b/contracts/okp4-cognitarium/src/contract.rs
index 74603966..43b8432f 100644
--- a/contracts/okp4-cognitarium/src/contract.rs
+++ b/contracts/okp4-cognitarium/src/contract.rs
@@ -97,7 +97,7 @@ pub mod query {
         VarOrNodeOrLiteral, WhereCondition, IRI,
     };
     use crate::querier::{PlanBuilder, QueryEngine};
-    use crate::rdf::{self, expand_uri, Atom, TripleWriter};
+    use crate::rdf::{self, expand_uri, Atom, Subject, TripleWriter};
 
     pub fn store(deps: Deps) -> StdResult<StoreResponse> {
         STORE.load(deps.storage).map(|s| s.into())
@@ -214,12 +214,13 @@ pub mod query {
             let subject = match subject_value {
                 Value::URI {
                     value: IRI::Full(uri),
-                } => uri,
+                } => Subject::NamedNode(uri),
                 Value::URI {
                     value: IRI::Prefixed(curie),
-                } => expand_uri(curie, &query.prefixes)?,
+                } => Subject::NamedNode(expand_uri(curie, &query.prefixes)?),
+                Value::BlankNode { value: id } => Subject::BlankNode(id.clone()),
                 _ => Err(StdError::generic_err(format!(
-                    "Unexpected value: {subject_value:?} (this was unexpected)"
+                    "Unexpected subject value: {subject_value:?} (this was unexpected)"
                 )))?,
             };
 
@@ -232,7 +233,7 @@ pub mod query {
                     value: IRI::Prefixed(curie),
                 } => expand_uri(curie, &query.prefixes)?,
                 _ => Err(StdError::generic_err(format!(
-                    "Unexpected value: {predicate_value:?} (this was unexpected)"
+                    "Unexpected predicate value: {predicate_value:?} (this was unexpected)"
                 )))?,
             };
 
@@ -266,7 +267,7 @@ pub mod query {
                 } => rdf::Value::LiteralDatatype(value, expand_uri(curie, &query.prefixes)?),
                 Value::BlankNode { value } => rdf::Value::BlankNode(value),
                 _ => Err(StdError::generic_err(format!(
-                    "Unexpected value: {object_value:?} (this was unexpected)"
+                    "Unexpected object value: {object_value:?} (this was unexpected)"
                 )))?,
             };
 
diff --git a/contracts/okp4-cognitarium/src/rdf/atom.rs b/contracts/okp4-cognitarium/src/rdf/atom.rs
index 6ffce2fc..e185c27c 100644
--- a/contracts/okp4-cognitarium/src/rdf/atom.rs
+++ b/contracts/okp4-cognitarium/src/rdf/atom.rs
@@ -1,3 +1,21 @@
+use rio_api::model::{Literal, NamedNode, Triple};
+use std::fmt;
+
+#[derive(Eq, PartialEq, Debug, Clone, Hash)]
+pub enum Subject {
+    NamedNode(String),
+    BlankNode(String),
+}
+
+impl fmt::Display for Subject {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Subject::NamedNode(s) => write!(f, "{s}"),
+            Subject::BlankNode(s) => write!(f, "{s}"),
+        }
+    }
+}
+
 #[derive(Eq, PartialEq, Debug, Clone, Hash)]
 pub enum Value {
     NamedNode(String),
@@ -7,9 +25,6 @@ pub enum Value {
     LiteralDatatype(String, String),
 }
 
-use std::fmt;
-
-use rio_api::model::{Literal, NamedNode, Triple};
 impl fmt::Display for Value {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -24,7 +39,7 @@ impl fmt::Display for Value {
 
 #[derive(Eq, PartialEq, Debug, Clone, Hash)]
 pub struct Atom {
-    pub subject: String,
+    pub subject: Subject,
     pub property: String,
     pub value: Value,
 }
@@ -42,8 +57,9 @@ impl std::fmt::Display for Atom {
 impl<'a> From<&'a Atom> for Triple<'a> {
     fn from(atom: &'a Atom) -> Self {
         Triple {
-            subject: NamedNode {
-                iri: atom.subject.as_str(),
+            subject: match &atom.subject {
+                Subject::NamedNode(s) => NamedNode { iri: s.as_str() },
+                Subject::BlankNode(s) => NamedNode { iri: s.as_str() },
             }
             .into(),
             predicate: NamedNode {