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We opened this chapter by defining the two types of databases currently used in database management: operational databases and analytical databases.

We then briefly discussed the hierarchical database model and the network database model. Our discussion covered the data structures, relationships, and data-access methods used in both models, as well as their chief disadvantages. You learned that these models were widely used in the early days of database management and led to the eventual development and introduction of the relational database model.

Next, we provided a detailed discussion of the relational database model, its history, and its features. We noted that it is based on specific branches of mathematics and that this mathematical foundation is what makes the model so structurally sound. Then we explored the model's data structures and relationships, and the role SQL plays in accessing data within the model. You'll remember, no doubt, that SQL is the standard language used to work with relational databases. We ended this section by reviewing the advantages of the relational database model.

We then took a look at a brief history of relational database management systems, beginning with the mainframe systems of the early 1970s and progressing through the PC-based systems of the 1980s to the client/server systems of the 1990s. At this point you should have a sense of the progression of circumstances that have led to the development of the database systems we use today.

The chapter continued with a brief discussion of the object-relational and object-oriented database models. Here you learned that these models emerged ostensibly as a means to deal with advanced database applications, and that they each incorporate various object-oriented elements and characteristics. You also learned that object-oriented databases are still in a state of flux and that debates still continue between object-oriented supporters and relational database proponents over the viability of object-oriented solutions.

Finally, we closed the chapter with a brief discussion of data warehouses and XML. You learned that data warehouses are used to consolidate and integrate data from heterogeneous sources and that the possibility of truly using them has only recently become more viable and practical. Next, you learned that XML is quickly becoming a de facto data transfer standard for sharing data across relational and nonrelational data sources. You also understand that relational databases are likely to be used for quite some time, despite the great impact the Internet has had on the way organizations use databases.

In the next chapter, we'll discuss why you should be concerned with database design and why theory is important. We'll also cover the objectives and advantages of good design.


Part II: The Design Process