diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/ExpressionContext.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/ExpressionContext.java
new file mode 100644
index 000000000..25d0df613
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/ExpressionContext.java
@@ -0,0 +1,27 @@
+package org.openrefine.wikidata.schema;
+
+import com.google.refine.model.Cell;
+import com.google.refine.model.ColumnModel;
+import com.google.refine.model.Row;
+
+
+public class ExpressionContext {
+    private String baseIRI;
+    private Row row;
+    private ColumnModel columnModel;
+    
+    public ExpressionContext(String baseIRI, Row row, ColumnModel columnModel) {
+        this.baseIRI = baseIRI;
+        this.row = row;
+        this.columnModel = columnModel;
+    }
+    
+    public String getBaseIRI() {
+        return baseIRI;
+    }
+    
+    public Cell getCellByName(String name) {
+        int idx = columnModel.getColumnByName(name).getCellIndex();
+        return row.getCell(idx);
+    }
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbChangeExpr.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbChangeExpr.java
new file mode 100644
index 000000000..a3eb4b587
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbChangeExpr.java
@@ -0,0 +1,10 @@
+package org.openrefine.wikidata.schema;
+
+import com.google.refine.Jsonizable;
+
+
+public interface WbChangeExpr extends Jsonizable {
+    /* Represents a change on an item: adding a statement,
+     * adding a label, adding a sitelink…
+     */
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbClaimExpr.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbClaimExpr.java
new file mode 100644
index 000000000..f4e41dea0
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbClaimExpr.java
@@ -0,0 +1,68 @@
+package org.openrefine.wikidata.schema;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+import org.wikidata.wdtk.datamodel.helpers.Datamodel;
+import org.wikidata.wdtk.datamodel.interfaces.Claim;
+import org.wikidata.wdtk.datamodel.interfaces.ItemIdValue;
+import org.wikidata.wdtk.datamodel.interfaces.Snak;
+import org.wikidata.wdtk.datamodel.interfaces.SnakGroup;
+import org.wikidata.wdtk.datamodel.interfaces.PropertyIdValue;
+
+
+public class WbClaimExpr implements WbChangeExpr {
+    
+    private WbItemExpr subjectExpr;
+    private WbSnakExpr mainSnakExpr;
+    private List<WbSnakExpr> qualifierExprs;
+    // TODO: references
+    
+
+    @Override
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        writer.object();
+        writer.key("subject");
+        subjectExpr.write(writer, options);
+        writer.key("mainsnak");
+        mainSnakExpr.write(writer, options);
+        writer.key("qualifiers");
+        writer.array();
+        for (WbSnakExpr expr : qualifierExprs) {
+            expr.write(writer, options);
+        }
+        writer.endArray();
+        writer.endObject();
+    }
+    
+    public static List<SnakGroup> groupSnaks(List<Snak> snaks) {
+        Map<PropertyIdValue, List<Snak> > map = new HashMap<PropertyIdValue, List<Snak>>();
+        for (Snak snak : snaks) {
+            PropertyIdValue pid = snak.getPropertyId();
+            if (!map.containsKey(pid)) {
+                map.put(pid, new ArrayList<Snak>());
+            }
+            map.get(pid).add(snak);
+        }
+        List<SnakGroup> snakGroups = new ArrayList<SnakGroup>();
+        for (List<Snak> snaksGroup : map.values()) {
+            snakGroups.add(Datamodel.makeSnakGroup(snaksGroup));
+        }
+        return snakGroups;
+    }
+    
+    public Claim evaluate(ExpressionContext ctxt) {
+        ItemIdValue subject = subjectExpr.evaluate(ctxt);
+        Snak mainSnak = mainSnakExpr.evaluate(ctxt);
+        List<Snak> qualifiers = new ArrayList<Snak>(qualifierExprs.size());
+        List<SnakGroup> groupedQualifiers = groupSnaks(qualifiers);
+        return Datamodel.makeClaim(subject, mainSnak, groupedQualifiers);
+    }
+
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemConstant.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemConstant.java
new file mode 100644
index 000000000..5efe60ab2
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemConstant.java
@@ -0,0 +1,39 @@
+package org.openrefine.wikidata.schema;
+
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+import org.wikidata.wdtk.datamodel.implementation.ItemIdValueImpl;
+import org.wikidata.wdtk.datamodel.interfaces.ItemIdValue;
+
+
+public class WbItemConstant implements WbItemExpr {
+    /* Represents an item that does not vary,
+     * it is independent of the row. */
+    
+    private String qid;
+    private String label;
+    
+    public WbItemConstant(String qid, String label) {
+        this.qid = qid;
+        this.label = label;
+    }
+
+    @Override
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        writer.object();
+        writer.key("qid");
+        writer.value(qid);
+        writer.key("label");
+        writer.value(label);
+        writer.endObject();
+    }
+
+    @Override
+    public ItemIdValue evaluate(ExpressionContext ctxt) {
+        return ItemIdValueImpl.create(qid, ctxt.getBaseIRI());
+    }
+
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemExpr.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemExpr.java
new file mode 100644
index 000000000..5c9e02341
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemExpr.java
@@ -0,0 +1,9 @@
+package org.openrefine.wikidata.schema;
+
+import org.openrefine.wikidata.schema.ExpressionContext;
+import org.openrefine.wikidata.schema.WbValueExpr;
+import org.wikidata.wdtk.datamodel.interfaces.ItemIdValue;
+
+public interface WbItemExpr extends WbValueExpr {
+    public ItemIdValue evaluate(ExpressionContext ctxt);
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemVariable.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemVariable.java
new file mode 100644
index 000000000..e6831108a
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbItemVariable.java
@@ -0,0 +1,42 @@
+package org.openrefine.wikidata.schema;
+
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+import org.wikidata.wdtk.datamodel.implementation.ItemIdValueImpl;
+import org.wikidata.wdtk.datamodel.interfaces.ItemIdValue;
+
+import com.google.refine.model.Cell;
+import com.google.refine.model.ReconCandidate;
+
+public class WbItemVariable implements WbItemExpr {
+    /* An item that depends on a reconciled value in a column */
+    
+    private String columnName;
+    
+    public WbItemVariable(String columnName) {
+        this.columnName = columnName;
+    }
+
+    @Override
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        writer.object();
+        writer.key("columnName");
+        writer.value(columnName);
+        writer.endObject();
+
+    }
+
+    @Override
+    public ItemIdValue evaluate(ExpressionContext ctxt) {
+        Cell cell = ctxt.getCellByName(columnName);
+        if (cell != null && cell.recon != null && cell.recon.match != null) {
+            ReconCandidate match = cell.recon.match;
+            return ItemIdValueImpl.create(match.id, ctxt.getBaseIRI());
+        }
+        return null;
+    }
+
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbPropConstant.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbPropConstant.java
new file mode 100644
index 000000000..2a3724428
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbPropConstant.java
@@ -0,0 +1,33 @@
+package org.openrefine.wikidata.schema;
+
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+import org.wikidata.wdtk.datamodel.implementation.PropertyIdValueImpl;
+import org.wikidata.wdtk.datamodel.interfaces.PropertyIdValue;
+
+
+public class WbPropConstant implements WbPropExpr {
+    /* A constant property, that does not change depending on the row */
+    
+    private String pid;
+    
+    public WbPropConstant(String pid) {
+        this.pid = pid;
+    }
+
+    @Override
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        writer.object();
+        writer.key("pid");
+        writer.value(pid);
+        writer.endObject();
+    }
+
+    @Override
+    public PropertyIdValue evaluate(ExpressionContext ctxt) {
+        return PropertyIdValueImpl.create(pid, ctxt.getBaseIRI());
+    }
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbPropExpr.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbPropExpr.java
new file mode 100644
index 000000000..fdf7a7300
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbPropExpr.java
@@ -0,0 +1,11 @@
+package org.openrefine.wikidata.schema;
+
+import org.wikidata.wdtk.datamodel.interfaces.PropertyIdValue;
+
+
+public interface WbPropExpr extends WbValueExpr {
+    /* An expression that represents a property */
+    
+    public PropertyIdValue evaluate(ExpressionContext ctxt);
+    
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbSnakExpr.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbSnakExpr.java
new file mode 100644
index 000000000..d282589ac
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbSnakExpr.java
@@ -0,0 +1,42 @@
+package org.openrefine.wikidata.schema;
+
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+import org.wikidata.wdtk.datamodel.helpers.Datamodel;
+import org.wikidata.wdtk.datamodel.interfaces.PropertyIdValue;
+import org.wikidata.wdtk.datamodel.interfaces.Snak;
+import org.wikidata.wdtk.datamodel.interfaces.Value;
+
+import com.google.refine.Jsonizable;
+
+
+public class WbSnakExpr implements Jsonizable {
+    
+    private WbPropExpr propExpr;
+    private WbValueExpr valueExpr;
+    
+    public WbSnakExpr(WbPropExpr propExpr, WbValueExpr valueExpr) {
+        this.propExpr = propExpr;
+        this.valueExpr = valueExpr;
+    }
+
+    @Override
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        writer.object();
+        writer.key("prop");
+        propExpr.write(writer, options);
+        writer.key("value");
+        valueExpr.write(writer, options);
+        writer.endObject();
+    }
+    
+    public Snak evaluate(ExpressionContext ctxt) {
+        PropertyIdValue propertyId = propExpr.evaluate(ctxt);
+        Value value = valueExpr.evaluate(ctxt);
+        return Datamodel.makeValueSnak(propertyId, value);
+    }
+
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbStringConstant.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbStringConstant.java
new file mode 100644
index 000000000..7844564c5
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbStringConstant.java
@@ -0,0 +1,34 @@
+package org.openrefine.wikidata.schema;
+
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+import org.wikidata.wdtk.datamodel.helpers.Datamodel;
+import org.wikidata.wdtk.datamodel.implementation.StringValueImpl;
+import org.wikidata.wdtk.datamodel.interfaces.Value;
+
+
+public class WbStringConstant implements WbValueExpr {
+    
+    private String value;
+    
+    public WbStringConstant(String value) {
+        this.value = value;
+    }
+
+    @Override
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        writer.object();
+        writer.key("value");
+        writer.value(value);
+        writer.endObject();
+    }
+
+    @Override
+    public Value evaluate(ExpressionContext ctxt) {
+        return Datamodel.makeStringValue(value);
+    }
+
+}
diff --git a/extensions/wikidata/src/org/openrefine/wikidata/schema/WbValueExpr.java b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbValueExpr.java
new file mode 100644
index 000000000..1e3970fec
--- /dev/null
+++ b/extensions/wikidata/src/org/openrefine/wikidata/schema/WbValueExpr.java
@@ -0,0 +1,16 @@
+package org.openrefine.wikidata.schema;
+
+import org.wikidata.wdtk.datamodel.interfaces.Value;
+
+import com.google.refine.Jsonizable;
+
+
+public interface WbValueExpr extends Jsonizable {
+    /* An expression that represents a Wikibase value,
+     * i.e. anything that can be on the right-hand side
+     * of a statement.
+     */
+    
+    public Value evaluate(ExpressionContext ctxt);
+    
+}