Add some notes

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 * Read "Chapter 9: Basic concepts of data warehousing"
 
+* data warehouse: a subject-oriented, integrated, time-variant, nonupdateable collection of data used in support of management decision-making processes.
+
+* subject oriented: organized around key subjects. e.g. customers, patients, students, products, and time.
+* integrated: data housed in the data warehouse are defined using consistent naming conventions, formats, encoding structures and related characteristics gathered from multiple sources.
+* time-variant: data in the data warehouse contain a time dimension so that they may be used to study trends and changes.
+* nonupdateable: loaded and refreshed from operational systems but cannot be updated by end users.
+
 ## Section 2 - Data Warehouse Architectures and OLAP Tools
 
 Read the Chapter 9 sections:
@@ -22,3 +29,14 @@ Read the Chapter 9 sections:
 * describe the process used to generate derived data;
 * describe the star schema, as used in data marts;
 * present a variety of tools and techniques that are used to query, analyze, and visualize the data stored in data warehouses and data marts.
+
+### Data Warehouse architectures
+
+* three-level architecture: bottom up, incremental approach
+* three-level architecture: top-down approach emphasis on coordination and an enterprise-wide perspective.
+
+1. extract data from internal/external sources. (daily, weekly, monthly)
+2. transform data.
+3. load data.
+
+I think I just fell asleep for several pages.