Beginning Database Design- P23 docx

The network model allows child tables to have more than one parent, thus creating a networked-like table structure.. Object database model —A model that provides a three-dimensional stru

Materialized view —A physically preconstructed view of data containing data copied into the material-ized view Materialmaterial-ized views can be highly efficient in read-only environments and are often used for replication, distribution and in data warehouses

Metadata —The tables and the fields defining the structure of the data; the data about the data

Method —The equivalent to a relational database stored procedure, except that it executes on the data contents of an object, within the bounds of that object

Microsoft Windows —The Microsoft Windows operating system

Multi-valued dependency —A field containing a comma-delimited list or collection of some kind A col-lection could be an array of values of the same type Those multiple values are dependent as a whole on the primary key, the whole meaning the entire collection in the comma-delimited list Each individual value is not dependent on the primary key

Nested query —A query executed from within another query In theory, queries can be nested up to any number of hierarchical layers The only limitation is on complexity and the abilities of the programmer

Network —A system of connected computers A local area network (LAN) is contained within a single company, in a single office A wide area network (WAN) is generally distributed across a geographical area — even globally The Internet is a very loosely connected network, meaning that it is usable by any-one and everyany-one

Network database model —Essentially a refinement of the hierarchical database model The network model allows child tables to have more than one parent, thus creating a networked-like table structure Multiple parent tables for each child allow for many-to-many relationships, in addition to one-to-many relationships

Non trivial multi-valued dependency —A multi-valued dependency with more than two fields in the

table (See Multi valued dependency.)

Non-identifying relationship —The child table is not dependent on the parent table, such that the child table includes the parent table primary key as a foreign key, but not as part of the child table’s primary key In other words, the parent record does not require, that a related record, exists in the child table A foreign key field can contain a NULLvalue, and it can’t be a part of the primary key because a primary key requires uniqueness

Normal Forms —The steps contained within the process of Normalization Normal Forms are cumulative, such that a database model in 3rd Normal Form is in both 2nd and 1st Normal Forms, but not Boyce-Codd (can be the same as 3rd Normal Form), 4th, 5th Normal Form, or Domain Key Normal Form

Normalization —The process of simplifying the structure of data Normalization increases granularity and Granularity is the scope of a definition for any particular thing The more granular a data model is, the easier it becomes to manage, up to a point, depending, of course, on the application of the database model

NOT NULLconstraint —A constraint that implies a field must have a value placed into it; otherwise, an error is returned

413 Glossary

NULL—A field that has never been initialized with any value ANULLfield setting allows a field to con-tain nothing when a record is created or changed in a table

Number —A numeric datatype allowing only numbers of various formats

Number crunching —Computer jargon for large quantities of extremely complex calculations

Object —In object methodology, the creation (instantiation) of a class at run-time, such that multiple object instances can be created from a class An object is also a generic term applied to anything tangible, such as a table in a relational database

Object database model —A model that provides a three-dimensional structure to data where any item

in a database can be retrieved from any point very rapidly Whereas the relational database model lends itself to retrieval of groups of records in two dimensions, the object database model is very efficient for finding unique items Consequently, the object database model performs very poorly when retrieving more than a single item, at which the relational database model is very good

Object-relational database model —The object-relational database model includes minimal aspects of the object database model into the relational database model In some respects, the object-relational database model was created in answer to conflicting capabilities of relational and object database models — and also

as a commercial competitor to the object database model The object database model is somewhat spherical

in nature, allowing access to unique elements anywhere within a database structure, with extremely high performance The object database model performs extremely poorly when retrieving more than a single data item The relational database model, on the other hand, contains records of data in tables across two dimensions The relational database model is best suited for retrieval of groups of data but can also be used

to access unique data items fairly efficiently

OLAP —See Online Analytical Processing.

OLTP —See Online Transaction Processing.

ONclause —The ONclause is an ANSI standard join format that allows exact field join specifications when you want to include one or more fields in a join, which have different names in different tables

One-to-many relationship —The relationship between two tables dictated by having one record in one table, and many related records in another table

One-to-one relationship —The relationship between two tables dictated by having one record in each table, and not more than one record in either table, related back to the other table

Online Analytical Processing (OLAP) —A functionality that provides rapid interactive analysis of data into multiple dimensions, usually involving extremely large databases The objective of analysis is to highlight trends, patterns and exceptions

Online Transaction Processing OLTP) —Databases that were devised to cater for the enormous concur-rency requirements of Internet (online) applications OLTP databases cause problems with concurconcur-rency The number of users that can be reached over the Internet is an unimaginable order of magnitude larger than that of an in-house company client-server database Thus, the concurrency requirements for OLTP database models explodes — well beyond the scope of previous experience with client-server databases

414

Glossary

Operating system —The lowest level of software on a computer, generally managing the interface and the hardware Windows, UNIX, and Linux are all operating systems

Operations —A term describing what a company does to make a profit

Optimizer —A term applied to a process, within a database engine, that attempts to find the fastest method of executing a SQL command against a database

ORDER BYclause —Query SELECTcommand adjustment allowing resorting (reordering) of records as they are returned from a query to a database

Outer join —An intersection plus rows outside the intersection, in one table and not in the other table of

a join

Overflow —A situation where new data is added to a table or index, but outside of the most effective structure, making subsequent reads potentially very inefficient Certain types of indexes are subject to overflow

Paper trail —The pieces of paper a company produces, and those passing through it, while it conducts its day-to-day affairs A company in the process of performing its day-to-day business is likely to have a paper trail of orders, invoices, bills, checks, and so on Analysis can gain copious amounts of information from a company paper trail Following the paper trail is a very useful method of gathering analytical details of the business operational processes of a company

Parallel processing —Execution of more than one thing at the same time, typically using multiple CPUs (but not always) Additionally, parallel processing used in hand with partitioning can result in some very effective performance improvements

Partitioning —Physical splitting of tables into separate sections (partitions), including parallel process-ing on multiple partitions and individual operations on individual partitions One particularly efficient aspect is the capability when querying a table to read fewer than all the partitions making up a table,

perhaps even a single partition This is also known as partition pruning.

Performance —Performance is a measure of how fast a database services applications, and ultimately end-users

Planning —A process whereby a project plan and timeline are used for larger projects Project plans typically include, who does what and when More sophisticated plans integrate multiple tasks, sharing them out among many people, ensuring dependencies are catered for For example, if task B requires completion of task A, the same person can do both tasks A and B If there is no dependency, two people can do both tasks A an B at the same time

Power-user —A user who is between an end-user and an expert computer programmer, in terms of knowing how to use a computer An end-user uses a computer as a tool to solve business problems

A computer programmer writes the software that end-users make use of A power user is someone in between, typically an end-user who writes his or her own software

Precedence —The order of resolution of an expression, and generally acts from left to right, across an expression

415 Glossary

Primary key —A key uniquely identifying each row in a table The entity on the many side of the rela-tionship has a foreign key The foreign key column contains primary key values of the entity on the one side of the relationship

Projection Normal Form (PJNF) —See 5th Normal Form.

Query —A statement interrogating the database and returning information Most often tables are inter-rogated and records from those tables are returned Queries can be both simple and complex A query is executed using the SQLSELECTcommand

Random access memory (RAM) —The memory chips inside your computer RAM provides an ultra-fast buffering storage area between CPU (the processor) and your I/O devices (disks)

RDBMS —See Relational Database Management System.

Record —A repetition of a field structure across a table Records repeat field structure in a table, where each repeated field can (and sometimes should) have a different value Tables are divided into fields and records Fields impose structure and datatype specifics onto each of the field values, in each record

Redundant Array of Inexpensive Disks (RAID) —A bunch of small, cheap disks A RAID array is a group of disks used together as a single unit logical disk RAID arrays can help with storage capacity, recoverability and performance, using what are called mirroring and striping Mirroring creates dupli-cate copies of all physical data Striping breaks data into many small pieces, where those small pieces can be accessed in parallel

Referential integrity —A process (usually contained within a relational database model) of validation between related primary and foreign key field values For example, a foreign key value cannot be added

to a table unless the related primary key value exists in the parent table Similarly, deleting a primary key value necessitates removing all records in subsidiary tables, containing that primary key value in foreign key fields Additionally, it follows that preventing the deletion of a primary key record is not allowed if a foreign key exists elsewhere

Relational Database Management System (RDBMS) —A system that uses a database that contains tables with data The management system part is the part allowing you access to that database, and the power to manipulate both the database and the data contained within it

Relational database model —A model that provides a two-dimensional structure to data The relational database model more or less throws out the window the concept and restriction of a hierarchical struc-ture, but does not completely abandon data hierarchies Any table can be accessed directly with having

to access all parent objects Precise data values (such as primary keys) are required to facilitate skirting the hierarchy (to find individual records) in specific tables

Replication —A method used to duplicate (replicate) and distribute data from a primary or master database, out to a number of other copies of the master database Those copies can be fully dependent slave databases, or even other master databases, capable of passing their own changes back

Right outer join —A query finding the combination of intersection, plus records in the right-sided table, but not in the left-sided table

416

Glossary

ROLLBACK—This command undoes any database changes not yet committed to the database using the COMMITcommand

SDK —Software development kit is a tool containing a programming language (Java, for example) SDKs are often used to build applications software

Secondary Index —See Alternate index.

SELECTcommand —A command used to execute a query on a database ASELECTcommand contains all the fields to be retrieved from tables Additionally, a SELECTcommand can have optional additions used to perform special alterations to queries, such as filtering using a WHEREclause, and sorting using

an ORDER BYclause

Self join —Joins records in a table to the same table Typically used for a table containing hierarchically structured records, such as a family tree

Semi-join —Join two tables using a subquery, but not necessarily returning any field values to the call-ing query Semi-joins occur when uscall-ing INand EXISTSoperators

Sequence —Allows automated generation of sequences of numbers, usually one after the other, such as

101, 102, 103, and so on Some database engines call these auto counters.

Simple datatype —A term used to describe the most basic of datatypes, containing a simple value, such

as an integer or a string

Snowflake schema —A data warehouse, single fact table structure, with dimension tables in multiple layered hierarchies of dimensional tables

Sorted query —SeeORDER BYclause.

SQL —See Structured Query Language.

Standby database —A failover database A standby database has minimal activity, usually only adding new records, changing existing records, and deleting existing records Some database engines, however, allow standby databases to be utilized as secondary, active database platforms

Star schema —A single fact table surrounded by a single hierarchical layer of dimensional tables, in a data warehouse database

Static data —Data that does not change significantly

Stored function —The same as a stored procedure, except that it returns a single value

Stored procedure —Also called a database procedure, a chunk of code stored within and executed from

within a database, typically on data stored in a database (but not always)

String —A simple datatype containing a sequence of alphanumeric characters

417 Glossary

Structured Query Language (SQL) —A non-procedural language that does not allow dependencies between successive commands SQL is the language used to access data in a relational database Generally, for any relational database other than Microsoft SQL-Server, SQL is pronounced “ess-queue-ell” and not

“sequel.”

Surrogate key —Used as a replacement or substitute for a descriptive primary key, allowing for better control, better structure, less storage space, more efficient indexing, and absolute surety of uniqueness Surrogate keys are usually integers, and usually automatically generated using auto counters or

sequences

Table —An entity that is divided into fields and records Fields impose structure and datatype specifics onto each of the field values in a record

Tertiary index —See Alternate index.

Time dimension —Used for temporal analysis in data warehouses

Timeline —For a project plan, a plotting of who does what and when A project plan and timeline are useful for larger projects Project plans typically include who does what and when More sophisticated plans integrate multiple tasks, sharing them out among many people, ensuring dependencies are catered for For example, if task B requires completion of task A, the same person can do both tasks A and B If there is no dependency, two people can do both tasks A an B at the same time

Timestamp —A datatype used to store date values, with a time of day attached as well

Transaction —In SQL, a sequence of one or more commands where changes are not as yet committed permanently to a database A transaction is completed once changes are committed or undone (rolled back)

Transactional control —A transaction is comprised of one or more database change commands, which make database changes A transaction is completed on the execution of a COMMITor ROLLBACKcommand, manually or automatically The concept of transactional control is that SQL allows sets of commands to be permanently stored all at once, or undone all at once

Transactional data —Data about the day-to-day dynamic activities of a company, such as invoices

Transitive dependence —Z is transitively dependent on X when X determines Y and Y determines Z Transitive dependence thus describes that Z is indirectly dependent on X through its relationship with Y

Trigger —A chunk of code that executes when a specified event occurs, usually before or after an INSERT, UPDATE, or DELETEcommand

Trivial multi-valued dependency —A multi-valued dependency with only two fields in the table (See

Multi valued dependency.)

Truncate —A term implying the removal of characters from a value, typically a number, where no rounding occurs

Tuple —See Record.

418

Glossary

Unique key —A key created on a field containing only unique values throughout an entire table.

UNIX —An operating system that is far more complex and far more difficult to manage than an operat-ing system like Microsoft Windows UNIX is, however, far more versatile and far more powerful but also much more expensive

UPDATE—The command used to change data in records in tables

Update anomaly —An error caused when a database allows an error to be generated, by updating incorrectly across a primary and foreign key relationship A record cannot be updated in a master table unless all sibling records, in all related child tables, are updated first Note that changes can be propa-gated to sibling records in child tables, using cascading

User —See End-user.

User-friendly —Describes a software application (or otherwise) that allows ease of use for the non-com-puter literate, or end-user population

Validation check — See Check constraint.

Variable-length records —Every record in a table does not have to be the same byte-length This allows use of datatypes, such as variable-length strings (CHAR VARYING(nn)) Most modern relational database engines use variable-length records

Variable-length string —A string with 0 or more characters, up to a maximum length of characters

View —A logical overlay containing a query, executed whenever the view is accessed Repeated query execution can make views very inefficient in busy environments

WHEREclause —A clause that is an optional part of the SELECTstatement, the UPDATE, and DELETE com-mands The WHEREclause allows inclusion of wanted records, and filtering out of unwanted records

Windows Explorer —A Microsoft Windows tool used to view and access files on disk

419 Glossary

A Exercise Answer s

This appendix contains all the answers to the exercises appearing at the ends of chapters

Chapter 3

Exercise 1 solution

Two CREATE TABLEcommands:

CREATE TABLE Band (

band_id INTEGER NOT NULL, band_name VARCHAR(32) NULL, CONSTRAINT XPK_Band PRIMARY KEY (band_id), CONSTRAINT XUK_B_Name UNIQUE (band_name) );

CREATE TABLE Track (

track_id INTEGER NOT NULL, band_id INTEGER NOT NULL, track_name VARCHAR(32) NULL, description VARCHAR(256) NULL, CONSTRAINT XPK_Track PRIMARY KEY (track_id), CONSTRAINT FK_T_Band FOREIGN KEY (band_id) REFERENCES Band, CONSTRAINT XUK_T_Name UNIQUE (track_name)

);

Exercise 2 solution

One CREATE INDEXcommand:

CREATE INDEX XFK_T_Band ON Track(band_id);

Chapter 4

Exercise 1 solution

Five CREATE TABLEcommands are shown here Note that the order in which tables are created is impor-tant, as assignment of foreign key columns requires that primary keys in parent tables already exist: CREATE TABLE Customer

(

customer_name VARCHAR(32) PRIMARY KEY, customer_address VARCHAR(256),

customer_phone VARCHAR(32) );

CREATE TABLE Stock_Source_Department

(

stock_source_department VARCHAR(32) PRIMARY KEY, stock_source_city VARCHAR(32) NOT NULL

);

CREATE TABLE Stock_Item

(

stock# INTEGER PRIMARY KEY, stock_source_department VARCHAR(32) NOT NULL REFERENCES Stock_Source_Department, stock_description VARCHAR(256),

stock_unit_price FLOAT );

CREATE TABLE Sale_Order

(

order# INTEGER PRIMARY KEY, customer_name VARCHAR(32) REFERENCES Customer, dte DATE,

sales_tax_percentage FLOAT );

CREATE TABLE Sale_Order_Item

(

order# INTEGER PRIMARY KEY, stock# INTEGER NOT NULL REFERENCES Sale_Order, stock_quantity INTEGER

);

Note how the PRIMARY KEYand FOREIGN KEYspecifications are included within the

specification of the column These are called in line constraint definitions This is a

different method of definition from that of exercises in Chapter 3 Chapter 3 uses

what are called out of line constraint definitions Inline constraint definitions can

only be used for constraints on single columns For example, a multiple column

primary key would have to be defined as an out of line constraint It is also possible

to define primary and foreign key constraints using an ALTER TABLEcommand to

change a table specification, after the table has already been created.

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Appendix A