UNORDERED TREE MATCHING AND TREE PATTERN QUERIES IN XML DATABASES

A stackable case assembly includes a plurality of cases. Each of the cases includes an outer case portion and an inner case portion. The outer case portion has one end face provided with a projection, with the other end face provided with a recess such that the projection can engage a recess of an adjacent case to allow stacking of a plurality of cases. The outer case further has a hollow middle portion. Positioning holes are respectively formed at upper and lower ends of the middle portion on an inner side in specific positions. The inner case portion is shaped to match the middle portion of the outer case portion, and has upper and lower ends respectively provided with a pivot in specific positions such that the inner case portion can be disposed in the middle portion of the outer case portion with the pivots engaging the positioning holes to allow the inner case portion to turn pivotally. The inner case portion can be opened or closed from one side of the outer case portion. The inner case portion further has a curved indentation at one end to facilitate to the user to exert a force to push the inner case portion away from the outer case portion, and a central portion that is recessed to form a receiving space to receive an article. The cases can be stacked to facilitate storage and display of articles without occupying much space.