COMP9318 Tutorial Week-3 - Data Warehouse and OLAP Q1.
(1) Create a star schema diagram that will enable FIT-WORLD GYM INC. to analyze their revenue.
The fact table will include – for every instance of revenue taken – attribute(s) useful for analyzing revenue; The star schema will include all dimensions that can be useful for analyzing revenue; and The only two data sources are shown in the next page.
(2) Appreciate the ETL process involved populating the data warehouse. (3) Appreciate the difference of formulating queries: “Find the percentage of revenue generated by members in the last year” . (4) How many cuboids are there in the complete data cube?
S1.
(1) As presented in the figures. Note that this is not the unique answer. (2) There are several tasks involved when importing the data into the data warehouse, e.g., we need to extract zipcode information from CorpCustNameLoc; we need to perform
aggregation [ price · Quantity] for tuples in the merchandise table; we might also need to deal with (near) duplicate object detection (e.g., the same “member” that appear in two data sources). (3) “Find the percentage of revenue generated by members in the last year” can be easily answered on the star schema by two aggregate queries on the fact table. Specifically, if the complete data cube has been built, the queries can be efficiently answered by the cuboid [Year ] , and the cuboid [Year,Category]. (4) Since CustName is not likely to be a good ”level” for analysis (rather, it is a descriptive attribute), there are 4 levels on Calendar dimension, 3 on Item, and 3 on Customer . Therefore, there are in total. Note that we could have different hierarchies on a dimension, e.g., we could consider the hierarchy on the Customer dimension one of the following. They have different semantics, but do not affect the number of cuboids.
Q2.
Suppose that a data warehouse consists of the three dimensions time, doctor , and patient , and the two measures count and charge, where charge is the fee that a doctor charges a patient for a visit. (1) Enumerate three classes of schemas that are popularly used for modeling data warehouses. (2) Draw a schema diagram for the above data warehouse using one of the schema classes listed in (1). (3) Starting with the base cuboid [day, doctor, patient ], what specific OLAP operations should be performed in order to list the total fee collected by each doctor in 2004? (4) To obtain the same list, write an SQL query assuming the data is stored in a relational database with the schema fee (day, month, year, doctor, hospital, patient, count, charge).
S2.
(1) Three classes of schemas popularly used for modeling data warehouses are the star schema, the snowflake schema, and the fact constellations schema. (2) A star schema is shown in the figure.
(3) The operations to be performed are:
Roll-up on time from day to year ;
Slice for time = 2004;
Roll-up on patient from individual patient to all.
(4) select doctor, SUM(charge) from fee where year = 2004 groupby doctor
