Tree builder

• Hierarchy of nodes
• Each node has a type and set of named properties
• Root of document represented by SD (SGML document) node
• Each element represented by EL node
• Children of EL node are content of element
• Each character represented by CH node
• Elements also have attributes represented by AT nodes.
• Element that has an AT node as an attribute called owner of that node.
• No ordering defined between AT nodes with same owner
• No representation of DTDs/LPDs
• Only one concurrent instance