Relational Database Design Tool and Mapping of 4NF And 5NF and ENHANCED ER TOOLS (EER) model Tool Generalisation

ENHANCED ER TOOLS

ER modeling concepts the EER model includes:
1) Subclass and Super class
2) Inheritance
3) Specialisation and Generalisation.
To describe the concepts of subclass and super class first let us revisit the concept of
‘entity’. The basic object that an E-R model represents is an entity, which is a “thing”
in the real world with an independent existence. An entity may be an object with a
physical existence or it may be an object with a conceptual existence. Each entity has
attributes (the particular properties that describe it).

Example : the entity vehicle describes the type (that is, the attributes and
relationship) of each vehicle entity and also refers to the current set of vehicle entities
in the showroom database. Some times to signify the database application various
meaningful sub-groupings of entity is done explicitly. For example, the members of
the entity vehicle are further meaningfully sub- grouped as: Car, Scooter, truck and so
on.
The set of entities in each of the groupings is a subset of the entities that belongs to
the entity set vehicle. In other words every sub-grouping must be vehicle. Therefore,
these sub-groupings are called a subclass of the vehicle entity type and the vehicle
itself is called the super class for each of these subclasses.
The relationship between a super class and any of its subclasses is called
class/subclass relationship. It is often called an IS-A or relationship because of the
way we refer to the concept, we say, “car is-a vehicle”. The member entity of the
subclass represents the same real world as the member entity of the super class. If
an entity is a member of a subclass, by default it must also become a member of
the super class whereas it is not necessary that every entity of the super class must
be a member of its subclass. From the discussion above on sub/super classes we
can say that an entity that is a member of a subclass inherits all the attributes of
9
Relational Database
Design
the entity as a member of the super class. Notice that the type of an entity is
defined by the attributes it possesses and the relationship types in which it
participates; therefore, the entity also inherits all the relationships in which the
super class participates. According to inheritance the subclass has its own
attributes and relationships together with all attributes and relationships it inherits
from the super class.

The process of defining the subclasses of an entity type is called specialisation,
where the entity type is called the super class of the specialisation. The above said
specialised set of subclasses are defined on the basis of some common but
distinguishing characteristics of the entities in the super class. For example, the set
of subclasses (car, scooter, truck) is a specialisation of the super class vehicle that
distinguished among vehicles entities based on the vehicle type of each entity. We
may have several other specialisations of the same entity type based on different
common but distinctive characteristics. Figure 2 shows how we can represent a
specialisation with the help of an EER diagram.



The subclasses that define a specialisation are attached by lines to a circle, which
is connected further with the super class. The circle connecting the super class
with the subclass indicates the direction of the super class/ subclass relationship.
The letter ‘d’ in the circle indicates that all these subclasses are disjoint
constraints.

Attributes that apply only to entities of a particular subclass – such as mileage of
car, stock of scooter and capacity of truck are attached to the rectangle
representing that subclass. Notice that an entity that belongs to a subclass
represents the same real-world entity as the entity connected to super class, even
though the same entity is shown twice − one in the subclass and the other in the
super class. A subclass is defined in order to group the entities to which these
attributes apply. The members of a subclass may still share the majority of their
attributes with the other members of the super class (as shown in Figure 3).


Hence the specialisation is a set of subclasses of an entity type, which establishes
additional specific attributes with each subclass and also establishes additional
specific relationship types between each subclass and other entity types or other
subclasses.

LEVELS OF DATABASE SECURITY

As is true for any other technology, the security of database management systems depends on many other systems. These primarily include the operating system, the applications that use the DBMS, services that interact with the DBMS, the web server that makes the application available to end users, etc. However, please note that most importantly, DBMS security depends on us, the-users.

Common Database Security Failures :Database security is of paramount importance for an organisation, but many organisations do not take this fact into consideration, till an eventual problem occurs. The common pitfalls that threaten database security are 

• Weak User Account Settings: Many of the database user accounts do not contain the user settings that may be found in operating system environments. For example, the user accounts name and passwords, which are commonly known, are not disabled or modified to prevent access.          The user account settings allow limited capabilities for security, without password controls on dictionary checks or account controls supporting expiration of user account. 
• Insufficient Segregation of Duties:No established security administrator role is defined in the database management of the organisation. This results in database administrators (DBAs) performing both the functions of the administrator (for users accounts), as well as the performance and operations expert. This may result in management inefficiencies 
• Inadequate Audit Trails:The auditing capabilities of databases since it require keeping track of additional requirements, are often ignored for enhanced performance or disk space. Inadequate auditing results in reduced accountability. It also reduces the effectiveness of data history analysis. The audit trails records information about the actions taken on certain critical of data. They log events directly associated with the data, thus, they are essential for monitoring the access and the activities on a database system. 
• Unused DBMS Security Features: The security of an individual application is usually independent of the security of the DBMS. Please note that security measures that are built into an application apply to users of the client software only. The DBMS itself and many other tools or utilities that can connect to the database directly through ODBC or any other protocol, may bypass this application level security completely. Thus, you must try to use security restrictions that are reliable, for instance, try using security mechanism that are defined within the database.

Basically database security can be broken down into the following levels:
• Server Security
• Database Connections
• Table Access Control
• Restricting Database Access.

1.  Server Security   Server security is the process of controlling access to the database server. This is the most important aspect of security and should be carefully planned. The basic idea here is “You cannot access what you do not see”.  For security purposes, you should never let your database server be visible to the world. If a database server is supplying information to a web server then it should be configured in such a manner that it is allowed connections from that web server only. Such a connection would require a trusted IP address. 
2. Trusted IP Addresses To connect to a server through a client machine, you would need to configure the server to allow access to only trusted IP addresses. You should know exactly who should be allowed to access your database server. For example, if it is the back end of a web server, then only that web server address should be allowed access to the database server. If the database server is the back end of a local application that is running on the internal network, then it should only talk to addresses from within the internal network. 
3. Database Connections With the ever-increasing number of Dynamic Applications, an application may allow immediate unauthenticated updates to some database. If you are going to allow users make updates to some database via a web page, please ensure that you validate all such updates. This will ensure that all updates are desirable and safe. For example, you may remove any possible SQL code from a user-supplied input. If a normal 
4. Table Access Control  Table access control is probably one of the most overlooked but one of the very strong forms of database security because of the difficulty in applying it. Using a table access control properly would require the collaboration of both the system administrator as well as the database developer. In practise, however such “collaboration” is relatively difficult to find. 
5. Restricting Database Access  By now we have defined some of the basic issues of database security, let us now look into the specifics of server security, from the point of view of network access of the system. Internet based databases have been the most recent targets of security attacks. All web-enabled applications listen to a number of ports. Cyber criminals often perform a simple “port scan” to look for ports that are open from the popular default ports used by database systems. How can we address this problem? We can address this problem “by default”, that is, we can change the default ports a database service would listen into. Thus, this is a very simple way to protect the DBMS from such criminals.

There are many ways of preventing open access from the Internet. Each DBMS and OS has its own set of unique features for the same. Let us discuss some general methods of preventing open access from the Internet.

• Trusted IP addresses : UNIX servers are configured to answer ping requests only from a list of trusted hosts. In UNIX, this can be accomplished by configuring the rhosts file. Thus, it restricts server access to a list of specific users only.

• Server Account Disabling : It may be a good idea to suspend the server ID after three failed password attempts. This may thwart attackers. If such a scheme is not implemented, then an attacker can run a brute force program that generates millions of passwords. Such a program ultimately would break the combination of the user ID and password.

• Special Tools : Some customised tools, for example, Real Secure, send an alert when an external server is attempting to breach your system security. There are many such similar products available for the protecting of the DBMS from unauthorised Internet access.