CSC310 quiz 1

Define/explain/give examples of these relational database terms: entity attribute relationship

-Entity is a distinct object (a person, place, thing, concept, or event) in the organization that is to be represented in the database: row -Attribute is a property that describes some aspect of the object that we wish to record: column -Relationship is an association between entities: is a, has a

Briefly, describe teleprocessing, file-server, two-tier client-server, and three-tier client-server architectures. For each one describe where the data is, and which computer(s) do the processing.

-teleprocessing: all processing done at mainframe, one computer does everything, impractical for huge transaction rates or huge numbers of users. -file serve: client PCs do most of the processing, large network traffic, concurrency; integrity; and failure recovery are more complex. -2 tier client server: client PCs with a database server. Decentralized by moving much processing off server/mainframe onto client PCs. User interface and main business logic handled by client. Server provides limited application logic (mostly validation, integrity, concurrency). Server's main job is query and update processing. Increased performance and more scalable than teleprocessing or file server setup. -3 tier client server: client, application server, database server. Over the last 10-15 years more widely used. Good for web-accessible system. Scalability greatly increased.

What are DDL and DML (what do the letters stand for, and briefly explanation each)?

DDL=data definition language- used by DBA to describe and name entities, attributes, relationships, integrity, and security constraints. Cannot be used to manipulate data. Processing DDL statements: creates database tables, stores definitions or metadata in the system catalog. DML=data manipulation language- used to manipulate the data by application programs, end-user queries. DML operations include insert a new row in a table (add data), modify data, retrieve data, delete data. DML includes a query language for retrieving data. 2 types= procedural language, non procedural/declarative language. Procedural refers to individual records/rows. Hierarchical DBMS and network DBMS use procedural DML embedded within a high-level programming language. Declarative refers to sets of records/rows. Relational DBMS uses SQL (a declarative DML). Standalone SQL DML. API for using SQL DML within a high-level programming language. Procedural specifies what output and how to retrieve the data, but declarative only specifies what output.

What is a web service?

Reusable code shared by multiple applications: can be written in one language and called from another language, can be called from applications running on a server or PC in faraway locations. No user interface. Functions/methods callable across a network or the internet. Callable from web pages or from standalone applications.

What are the three levels or layers of the ANSI Database Architecture? Besides knowing their names, briefly, explain what they are.

external level- multiple users' views of the database, each user can have a different view, views are independent of how data is physically stored conceptual level- community view of entire database, describes all data in the database and relationships among the data, view is independent of how data is physically stored internal level- how the data is stored in the database, how the data is physically stored in the hardware on the computer(s)

List & explain some of the problems or limitations of a file-based system, that are eliminated or improved with a database approach. Another way to ask this would be to ask for advantages of DBMS over file-based systems. The book lists 5 main disadvantages. Know at least 3!

incompatible file formats-different programs written in different languages data separation/isolation- each program maintains its own data file(s) data redundancy- same data in more than one file data dependence- file structure is defined in program code

What is a system catalog for a dbms? (What kind of stuff is in such a catalog?)

the description of the data is known as the system catalog -stores definitions or metadata for processing DDL statements

In the context of a database or dbms what is a transaction? What does it mean for the dbms to provide transaction support?

transaction=series of actions carried out by a single user or application program which accesses or changes the contents of the database. transaction support=a DBMS must furnish a mechanism that will ensure either all of the updates corresponding to a given transaction are made or that none of them are made.