8. The method of claim 1 , wherein the particular portion is at least part of a first document, wherein the expression is a first expression, wherein the value is a first value, and wherein the location is a first location, the method comprising: receiving a second expression that specifies a second value; determining that the unstructured database column in the database stores a second document, wherein the second document comprises non-marked up text that contains the specified value; determining a second location of the second document; and accessing the second document from the second location.
8. The method of claim 1 , wherein the particular portion is at least part of a first document, wherein the expression is a first expression, wherein the value is a first value, and wherein the location is a first location, the method comprising: receiving a second expression that specifies a second value; determining that the unstructured database column in the database stores a second document, wherein the second document comprises non-marked up text that contains the specified value; determining a second location of the second document; and accessing the second document from the second location. 9. The method of claim 8 , further comprising rewriting the second expression to reference a virtual node that represents the second document, wherein the virtual node does not appear in the second expression, and wherein the virtual node does not appear in the second document.