ObjectStore is an object-oriented database system supporting persistence orthogonal to type, transaction management, and associative queries. Collections are provided as objects. The data model is non-1NF, as objects may have embedded collections. Queries are integrated with the host language in the form of query operators whose operands are a collection and a predicate. The predicate may itself contain a (nested) query operating on an embedded collection. Indexes on paths may be added and removed dynamically. Collections, being treated as objects, may be referred to indirectly, e.g., through a by-reference argument. For this reason and others, multiple execution strategies are generated, and a final selection is made just prior to query execution. Nested queries can result in interleaved execution and strategy selection.