**2.3 Amending query**

A query that only request a key attribute of a relation from a remote server to extract known available data from cache is called an amending query. When we know that some data is available in semantic cache but could not extract it precisely. Than we request the server for a key attribute for a user query and extract cached attributes (data) against those keys from cache. Requesting only keys require less computation on database server and low bandwidth over network, in general.

Consider the following employee database information provided in example 1 below, which shall be used throughout evaluation in this chapters. The semantic cache model we follow is similar to the relational database model. The basic building blocks of the relational model are attributes (columns), rows (tuple), tables (relations) and relation schema. The schema defines the relations and the attributes with their data type in each relation. A row or a tuple is a set of attribute's instances.

#### **2.4 Example 1**

Consider an employee database with a relation name *Emp (Empid, Ename,Department, Age, Salary,Exp)*. The domain of the *Age, Salary*, *Department* and *Exp* attributes of *Emp* are {20,…,100},{0.1K,…,1K,…15K},{CS, EE, BI, BA},{1,..,50} respectively as shown in Figure 2. Also suppose that a cache already has following cached queries shown in Figure 3.
