System and method for storing and searching buy and sell information of a marketplace

A method of accessing a database using a computer system. One example of the method includes the following steps. Access a tree data structure. The tree data structure includes a set of nodes linked in parent, child and sibling relations. Each node of a subset of nodes is associated with a corresponding term. Select some nodes of the set of nodes. This includes selecting a node of the set of nodes. The node has at least a sibling node. In response to selecting the node, performing one of the following actions. If the node is a first type of node, allowing a selection of the sibling node. If the node is a second type of node, not allowing a selection of the sibling node. Record a list of node selections corresponding to the selection of some nodes. Extract a set of terms from the list of node selections. Create a data structure including price information and duration of existence information. Store the data structure in the database using the set of terms. The data structures in the database can be accessed and analyzed.