Codds Rules Powerpoint Presentation1

7/22/2019 Codds Rules Powerpoint Presentation1

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Codds Twelve Rules

Rules that a DBMS should

follow to be classified asfully relational


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Oracles grading scale

0 = doesnt meetcriteria

1/2 = meets some ofthe criteria

1 = meets the criteria


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1. Information Rule

information is to be represented as datastored in cells

Vehicle Identification Number in one cellwould violate this rule

paint color

body style


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2. Guaranteed access rule

Each data item must be accessible bycombination of

table name + primary key of row +columnname

violation of rule--ability to access by usingarrays or pointers


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How does Oracle fair on

the 1st two points??

BLOBs-Binary Large OBjectsearly RDBMS technique to store and manage

multimedia data types

typically stored outside the database (in files), and

pointers are placed in their corresponding columnpositions

BLOBs push the 1st two rules

Implementation is transparent to the user

Do not explicitly break 1st two rulesScore 1 1/21/2 pt deducted for bad conduct

competitors grade out the same


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3. Nulls must be used in a

consistent manner

Violation--0 used as value for missingnumbers and blank for missing character

valuescorrect way--nulls simply be missing data

and have no values

If values are desired for missing data,vendors usually offer the ability to usedefaultsfor this purpose.


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Grade for rule 3

1/2

current implementation for nulls in SQL is

poor for all vendorshas been attacked by Codd and another

relational pioneer, C. J. Date

Codd proposes 3 valued logic

Date proposes abolishing of nulls altogether

some very real data problems with the use ofNULLs today in RDBMSs.


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4. An active, online data

dictionary should be stored

as relational tables andaccessible through the

regular data access

language.

If any part of the data dictionary is stored

in the operating system, this rule wouldbe violated.


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Grade for rule 4

1/2

Oracle allows SELECT only, but INSERT,

UPDATE, and DELETE are not possibleThis probably should not occur frequently

and may not even be desired, but it should

be possible according to rule 4.


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6. All views that may be

updatable should beupdatable.

If, for example, you could join threetables as the basis for a view, but not beable to update that view, then this rule

would be violated.


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Rule 6 Grade

1/2

Improved for version 8 over 7

Version 8 is not 100% compliant

7 Th t b t l l


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7. There must be set-level

inserts, updates, and

deletes.

Currently, this is provided by most RDBMSvendors to some degree.


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8. Physical data

independence.

An application cannot depend on physicalrestructuring. If a file supporting table

was moved from one disk to another, orrenamed, then this should have no impacton the application.


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9. Logical data

independence.

How a User views data should not changewhen the logical structure (tables

structure) of the database changes.This rule is particularly difficult to satisfy.

Most databases rely on strong tiesbetween the user view of the data andthe actual structure of the underlyingtables.


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10. Integrity independence.

Integrity rules should be stored in thedata dictionary. Primary key constraints,

foreign key constraints, check constraints,triggers, and so forth should all be storedin the data dictionary.


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11. Distribution dependence.

A database should continue to workproperly even if distributed (extension of

rule 8 -- except rather than only beingdistributed on a single system (locally), adatabase may also be distributed across a

network of systems (remotely).


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Rule 11 Grade

1/2

Oracle does offer

database links, snapshots, symmetric replication, and distributed

database with a two-phase commit (2PC).

Some of the networking is user-apparent, 2PC works butnot well, and replication has its own problems

Majority of complaints center on the fact that all these

capabilities require the user to know more than oneshould have to know about the setup behind thetechnology


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12. The nonsubversion rule.

If low-level access is allowed, it must not bypasssecurity nor integrity rules, which would otherwise beobeyed by the regular data access language. A backup

or load utility, for example, should not be able to bypassauthentication, constraints, and locks. However,vendors often provide these abilities for the sake ofspeed. It is then the DBAs responsibility to ensure thatsecurity and integrity, if momentarily compromised, arereinstated. An example is disabling and re-enablingconstraints for a VLDB load.


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Through some of its utilities, such asSQL*Loader and Import, Oracle allows

data to be stored in the database bybypassing the standard SQL route,opening up the database to potentialcorruption


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Final Grade

8 1/2 out of 12

give or take a point

Point is not the precision of final score

FACT--Oracle does not meet all of Codds

12 rules

Neither does Sybase nor Informix

It is a RDBMS

Oracle and its competitors have more workto do

Oracle 7 only fully passed rule 10


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Codds Rule Zero

For a system to qualify as a RDBMS, thatsystem must use its relational facilities

exclusively to manage the database.Meet all fundamentals discussed in

relational database chapter and these 12

rules --- database may be designated asrelational

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Codds Rules Powerpoint Presentation1