A Phase-to-Phase Guide to the Duwamish Books Data Access Strategy

	Phase 1 Application Code Schema-aware code accesses data: • Access SQL (Select, Insert, and Update) • ISAM-style data manipulation (AddNew . . . Update) Data Access Code in the desktop applications • ADO 1.5 • Access ODBC driver Database Microsoft Access 97 .mdb file format database Simple schema representing business model (not highly normalized) Read "Designing a Simple Retail-Oriented Database"

	Phase 2 Application Code Access data through Data Access Layer API DAL.ExecQuery and GetRecordset (schema-aware Access SQL) TransactedRecordset (ISAM-style for transactions requiring multiple trips) Data Access Data access code broken out into Data Access Layer (DAL) component • ExecQuery, GetRecordset, TransactRecordset • ADO 1.5 • Access ODBC driver Database Database schema extended to support multiple stores Schema modifications at inventory hot spot Read "Designing a Data Access Layer" "Modeling a Distributed Inventory: Duwamish Books, Phase 2" "Breaking Out the Data Access Layer" "Duwamish Books Data Access Layer API, Phase 2" "Migrating a Visual Basic 5.0 Component to Visual C++ 5.0"

	Phase 3 Application Code All data access through Business Logic Layer API (GetCustomer, InsertOrder, . . .) ADO 2.0 hierarchical disconnected recordsets Business Logic Business logic broken out into Business Logic Layer (BLL) component • API encapsulates database schema • Executes stored procedures in the database through the DAL. • Minimizes round trips and maximizes scalability. Data Access SQL Server ODBC driver ADO 2.0. DAL API revised to simplify complex transactions Database SQL Server 6.5 Stored procedures used exclusively for all data access and manipulation Simple Phase 2 schema remains Read "Migrating the Duwamish Books Database to SQL Server" "Duwamish Data Access Layer Shifts into Phase 3" "Abstracting Business Transactions" Phase 3.5 Business Logic OLE Transactions brokered by MTS Data Access MTS takes over management of ADO/ODBC connection(s) Read "Moving a Data Access Layer into Microsoft Transaction Server" "Distributing Duwamish Books with Microsoft Transaction Server" "Remoting Duwamish Components" "Hoisting the Duwamish Components into MTS"

	Phase 4 Presentation Layer Three client types (HTML 3.2, Internet Explorer 4.0 DHTML with data binding , and Internet Explorer 5 DHTML, XML/XSL) XMLDOM transforms XML data to HTML using XSL for separation of data and presentation Workflow Layer Cache infrequently changing data as XML/HTML Transform data from ADO 2.1 disconnected recordsets to XML Store user context data as XML in location-independent manner (cookie, session state, or back end) Business Logic Layer Revised interfaces optimized for scalability Microsoft English Query transforms English to SQL Data Access SQL Server ODBC driver ADO 2.1 MTS manages ADO/ODBC connection(s) Database SQL Server 7.0 Modified schema for increased scalability and performance Read "Data Flow Through Duwamish Books" "Three Approaches for Three Client Types" "Workflow Design for a Web Commerce Application" "Creating a Page Cache Object"