Prepare Sample Data Files

These steps involve preparing sample data files for the

Database Designer to use in producing the

Physical Schema design. If your actual data files are available at this point, you can use a subset of the full data set as sample data. Otherwise, you can use data generated by a commercial data generator application.

A physical schema consists of a set of projections used to store data on disk. The projections in the physical schema are based on the objects in the Logical Schema.

The Database Designer is a tool that analyzes a logical schema definition, sample queries, and sample data and generates a set of projections in the form of an SQL script to be executed after you create the tables but before you load any data. The script creates a minimal set of superprojections to ensure K-Safety, and optionally pre-join projections. In most cases, the projections created by the Database Designer provide excellent query performance within physical constraints. You can, however, write a custom projection script should the Database Designer not meet your needs.

The Database Designer can read up to one hundred thousand (100K) rows of data (1000 uniform seeks reading 100 rows at a time) of sample fact table data. If there are 100K or fewer rows in the sample data file, all rows are sampled. If the data file is larger, the sampling is uniformly distributed to avoid skew problems. (An internal cycle in the data may cause skew problems but is unlikely.)

Name each data file to match the corresponding table in the logical schema. Case does not matter. Use the extension .tbl or whatever you prefer. For example, if a table is named Stock_Dimension, name the corresponding data file stock_dimension.tbl. When using multiple data files, append _nnn (where nnn is a positive integer in the range 001 to 999) to the filename. For example, stock_dimension.tbl_001, stock_dimension.tbl_002, etc.