Formal languages play a central role in the Semantic Web. An important aspect regarding their design is syntax as it plays a crucial role in the wide acceptance of the Semantic Web approach. The main advantage of controlled natural languages (CNL) is to reconcile the high-level and natural syntax of natural languages, and the precision and lack of ambiguity of formal languages. In the context of the Semantic Web and Linked Open Data, CNL could not only allow more people to contribute by abstracting from the low-level details, but also make experienced people more productive, and make the produced documents easier to share and maintain. We introduce SQUALL, a controlled natural language for querying and updating RDF graphs. It has a strong adequacy with RDF, an expressiveness close to SPARQL 1.1, and a CNL syntax that completely abstracts from low-level notions such as bindings and relational algebra. We formally define the syntax and semantics of SQUALL as a Montague grammar, and its translation to SPARQL. It features disjunction, negation, quantifiers, built-in predicates, aggregations with grouping, and n-ary relations through reification.