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 Components of ERD


Entities : An entity is something about which the business needs to store data. An entity is a class of persons, places, objects, events or concepts about which we need to capture and store data. An entity instance is a single occurrence of an entity.

Attribute: An attribute is a descriptive property or characteristic of an entity. Synonyms include element, property and field. A compound attribute is one that actually consists of other attributes. It is also known as a composite attribute. An attribute “Address” is the example of compound attribute as shown in the following illustration

Relationships: A relationship is a natural business association that exists between one or more entities. The relationship may represent an event that links the entities.

Cardinality: defines the minimum and maximum number of occurrences of one entity that may be related to a single occurrence of the other entity. Because all relationships are bidirectional, cardinality must be defined in both directions for every relationship.

A DFD can be categorized in the following forms:ny system can be represented at any level of detail by these four symbols.

External Entities

External Entity

External entities determine the system boundary. They are external to the system being studied. They are often beyond the area of influence of the developer.These can represent another system or subsystem. These go on margins/edges of data flow diagram. External entities are named with appropriate name.

Processes

DFD Process

Processes are work or actions performed on incoming data flows to produce outgoing data flows. These show data transformation or change. Data coming into a process must be “worked on” or transformed in some way. Thus, all processes must have inputs and outputs. In some (rare) cases, data inputs or outputs will only be shown at more detailed levels of the diagrams. Each process in always “running” and ready to accept data.Major functions of processes are computations and making decisions. Each process may have dramatically different timing: yearly, weekly, daily.

Naming Processes

Processes are named with one carefully chosen verb and an object of the verb. There is no subject. Name is not to include the word “process”. Each process should represent one function or action. If there is an “and” in the name, you likely have more than one function (and process). For example, get invoice ,update customer and create Order Processes are numbered within the diagram as convenient. Levels of detail are shown by decimal notation. For example, top level process would be Process 14, next level of detail Processes 14.1-14.4, and next level with Processes 14.3.1-14.3.6. Processes should generally move from top to bottom and left to right.

Data Flow

DFD Data Flow

Data flow represents the input (or output) of data to (or from) a process (“data in motion”). Data flows only data, not control. Represent the minimum essential data the process needs. Using only the minimum essential data reduces the dependence between processes. Data flows must begin and/or end at a process.Data flows are always named. Name is not to include the word “data”. Should be given unique names. Names should be some identifying noun. For example, order, payment, complaint.

Data Stores

Data Store

or

Data Store

Data Stores are repository for data that are temporarily or permanently recorded within the system. It is an “inventory” of data. These are common link between data and process models. Only processes may connect with data stores.There can be two or more systems that share a data store. This can occur in the case of one system updating the data store, while the other system only accesses the data.

Context diagrams 
An overview of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the entities and the system. In this diagram, a single process represents the whole system.

First level DFD: A data flow diagram that represents a system’s major processes, data flows, and data stores at a high level of detail.

CSS handles the look and feel part of a web page. Using CSS the color of the text, the style of fonts, the spacing between paragraphs, how columns are sized and laid out, what background images or colors are used, layout designs, variations in display for different devices and screen sizes as well as a variety of other effects. CSS provides powerful control over the presentation of an HTML document. Most commonly, CSS is combined with the markup languages HTML or XHTML.

  1. You can define a style for each HTML element and apply it to as many Web pages as you want.
  2. You do not need to write HTML tag attributes every time. Just write one CSS rule of a tag and apply it to all the occurrences of that tag.
  3. CSS simply change the style, and all elements in all the web pages will be updated automatically.
  4. CSS using the same HTML document, different versions of a website can be presented for handheld devices such as PDAs and cell phones or for printing.
  5. Its a good idea to start using CSS in all the HTML pages to make them compatible to future browsers.

 Java is an object-oriented programming language, we have to follow the encapsulation wherein we hide the unwanted details.

Java provides entities called “Access Modifiers or access specifiers” that help us to restrict the scope or visibility of a package, class, constructor, methods, variables, or other data members. These access modifiers are also called “Visibility Specifiers”.

Access Modifiers In Java
To ensure encapsulation and reusability, these access specifiers/modifiers are an integral part of object-oriented programming.


Modifiers in Java are of two types:

#1) Access Modifiers

Access modifiers in Java allow us to set the scope or accessibility or visibility of a data member be it a field, constructor, class, or method.

#2) Non-access Modifiers

Java also provides non-access specifiers that are used with classes, variables, methods, constructors, etc. The non-access specifiers/modifiers define the behavior of the entities to the JVM.

Some of the non-access specifiers/modifiers in Java are:

  • static
  • final
  • abstract
  • transient
  • volatile
  • synchronized
  • native
    

Types Of Access Modifiers In Java

Java provides four types of access specifiers that we can use with classes and other entities.

These are:

#1) Default: Whenever a specific access level is not specified, then it is assumed to be ‘default’. The scope of the default level is within the package.

#2) Public: This is the most common access level and whenever the public access specifier is used with an entity, that particular entity is accessible throughout from within or outside the class, within or outside the package, etc.

#3) Protected: The protected access level has a scope that is within the package. A protected entity is also accessible outside the package through inherited class or child class.

#4) Private: When an entity is private, then this entity cannot be accessed outside the class. A private entity can only be accessible from within the class






 

 

 


 A time series is simply a series of data points ordered in time. In a time series, time is often the independent variable and the goal is usually to make a forecast for the future.

We wish to predict the trend in financial markets or electricity consumption, time is an important factor that must now be considered in our models