u | tree structure |
| u | one to one and one to many relationships
u | objects grouped in container |
| u | express relationship directly |
| u | implicit acess path to the data |
u | multiple relationships |
| u | links of specific semantics |
u | occurance operator |
| u | allow various instances |
| matching one DTD |
| u | useful for subclassing |
u | Inheritance |
| u | by reference |
| u | by position |