1.1 Introduction - The Unseen Services

In today's modern societies, we depend on many services that come from organizations and governments, and we take these services for granted. Often we are not even aware of the underlying and invisible components that make these services available to us. For example, we live in houses, work and go to school in buildings, exercise in gymnasiums, and go to sports activities in stadiums. We observe and interact with the visible elements of these edifices, but we seldom think about the unseen components that provide us comfort and stability.

Just as edifices contain both visible structures and an unseen infrastructure, the services that we use extensively every day also include these two separate components. We use our smartphones for all types of activities. We receive services such as the internet from our computers. We obtain services from people and companies as we shop, go to the doctor, or get a driver's license. The unseen components of all these activities are the databases that provide support in our information-rich, connected, and mobile world. Of course, almost everything we do with electronic devices depends on some underlying databases. In most cases, we do not even think about the source and format of the information that we are retrieving.

Let's examine some examples:

• Log in and use Facebook:  Your login and personal information is kept in a database, as is the information for all of your friends, posts, and messages.

• Make a phone call or send a text message:  The lists of phone numbers and locations in your cell phone is maintained by databases. All the information about your phone calls and text messages is maintained at a very detailed level in databases.

• Read your email:  Not only is your login information kept in a database, but also all the history of incoming and outgoing emails is kept in very large databases.

• Go shopping (groceries, clothes, gasoline):  First, the product, inventory levels, and price information is kept in a database so that the checkout register can identify it correctly. Then (if you use a credit or debit card), that information must be retrieved from another database.

• Check a book out of the library:  The database is checked to make sure you are a valid patron of the library. Then, information about the book, its availability, and checkout status is all verified and updated for your library loan. The database is used to obtain both patron information and book information.

• Withdraw money from an ATM:  First, your authorization information must be verified, and then the availability of sufficient funds is also verified. Finally, your account balances must be updated. All this information is stored in the bank's databases.

• Have a physical exam with your doctor:  All of your patient information is maintained in your medical database. Your records will be updated from the results of your exam. The accounting, billing, and insurance records will also all be updated.

We seldom think about these databases unless they become unavailable or there has been a security breach where private data has been accessed by unauthorized individuals or been made public. When databases don't work correctly, we get frustrated and upset that the level of service that we expect is not being provided. The availability and integrity of databases is an important issue in the daily activities of each of our lives.