i think the answer to your aggregation q is yes. this is not formal uml, but:
"Consider the difference between object aggregation and acquaintance . . . . Aggregation implies that one object owns or is responsible for another object. Generally, we speak of an object having or being a part of another object. Aggegation implies that an aggregate object and its owner have identical lifetimes. Acquaintance implies that an object merely knows of another object. Sometimes acquaintance is called association or the using relationship. Acquainted objects may request operations on each other, but they aren't responsible for each other. Acquaintance is a weaker relationship and suggests much looser coupling between objects. In our diagrams, a plain arrowhead line denotes acquaintance. An arrowhead line with a diamond at its base denotes aggregation." p23 Design Patterns, Gamma, et al