CREATION AND DEVELOPMENT OF HOUSING DEMAND MODEL

ABSTRACT

The article is devoted to the creation and development of a model of demand for housing. A web application has been created that allows users to view advertisements for rental and sale of housing, with the analysis of optimal prices for the current period. The web application was created using the following technologies: Java, Spring, JPA, SQL, HTML, Java Script, JQery. The web application has the ability to register users, log in to the system, create, edit ads, download images for ads with automatic change of permissions, search by parameters, create prices.

Keywords: information system, algorithm, web application, database, technology, client part, server part, entities, packages, framework, interface.

1. Introduction

Model - an object-substitute of the original object, providing the study of some properties of the latter; simplified representation of the system for its analysis and prediction, as well as obtaining qualitative and quantitative results necessary for making the right managerial decision [1]. Demand is the amount of goods and services that buyers are willing to purchase at a given time, in a given place, at given prices.

The architecture of the Information System - a set of significant decisions regarding the organization of the software system, a set of structural elements and their interfaces, with which the system is linked together with their behavior, defined in the interaction between these elements, the layout of the elements into gradually enlarged subsystems, as well as the style of architecture, which directs this organization (elements and their interfaces, interaction and layout) [2]. In order to implement a web application, you will need to produce a building architecture.

The work is devoted to the creation of a web application that allows buyers to buy or rent housing, and tenants and sellers - to place ads. To create a web application, special technologies and capabilities were used, which will be discussed in detail.

2. Component web applications.

The application can conditionally be divided into several layers - the client part (frontend), the server part (backend) and the database. Consider each layer.

A database is an organized structure designed to store, modify and process interconnected information, mainly of large volumes. In the context of databases, it is worth considering the concept of a DBMS (database management system). DBMS is a complex of software tools necessary for creating the structure of a new database, filling it, editing content and displaying information. [3].

The Opengas solution PostgreSQL was taken as a database management system. The database is used exclusively for data storage and does not store business logic operations in the form of stored procedures. The data scheme consists of 4 tables: rsrt_ads for storing ads, rsrt_ad_images for image information for each ad, rsrt_price_tags for storing prices and rsrt_users for users (Figure 1). All information that is in the database is displayed in the client part. In this case, the user can add information, edit and delete, respectively, all changes are saved in the database.

Figure 1. Database structure

The server part is implemented in Java using the Spring framework - one of the most popular frameworks for creating web applications in Java. A framework is something like a library. Roughly speaking, using the library, the objects of the classes that are in it are created, only the necessary methods are called, and thus the result is obtained. That is, in a web application at what specific moment you need to create which object, at what moment to call a specific method. And with the help of the framework, these actions are much easier. Classes are created in the web application that describe part of the logic, and the framework itself creates class objects and calls methods. Classes implement interfaces from the framework or inherit other classes from it, thus getting some of the functionality already written. In Spring, for example, they try to get as far as possible from such tight connectivity (when classes directly depend on some classes / interfaces from this framework), and use annotations for this purpose.

The server side code is conditionally divided into several layers or packages - core, dataproviders, entrypoints, propertyproviders, security and configuration. Core contains business logic, dataproviders - database access code, entrypoints - entry points for client code, propertyproviders - access to some application properties, security and configuration - application and security settings. The application accesses the database using the Hibernate library (JPA, java classes are put in one-to-one correspondence with the database tables).

The client part consists of HTML pages that are dynamically formed using the thymeleaf template engine. The template engine allows you to transfer values calculated by the server side to html pages. Ajax elements are also used to exchange information with the server.

3. Application architecture.

Let's see how backend-e code is organized. The code is organized in accordance with the dependency rule [4] (Figure 2). In the figure, the circles represent different levels of pragmatic support. The closer to the center, the higher the level. The rule of dependencies can be formulated as follows: dependencies in the source code should be directed inward, towards higher-level policies. Nothing in the inner circle knows anything about the outer circles. Briefly consider each level.

Entities embody critical business rules. Entities are java classes - Ad (ad), AdImage (image of ad), HousingType (type of housing), Pricetag (price tag), User (user). These classes are inside the core.domain package.

Use cases are business rules specific to the application. This level of the Information System encapsulates and implements all options for using the system. Packages - core.usecase, core.properties, core.constants. An example of use cases is to activate an ad, find ads for a specific user, etc.

An information system at this level is a set of adapters that convert data from a format that is most convenient for use cases and entities to a format that is most convenient for some external agents, such as a database or web interface. Packages - dataproviders, entrypoints, configuration, propertiesproviders, security. For example, the PricetagDataProvider class is a database access gateway. Data format convenient for business rules - PriceTag class; Database-friendly format - PricetagEntity (uses the JPA engine); an adapter that converts the two previous formats to each other - PricetagEntityConverter. In case we want to change the database with Postgresql, for example, on mongodb we need to change only two classes - PriceTagEntity and PriceTagDataProvider. Such organization of the code simplifies the maintenance of the system (which means it makes it cheaper) and making changes, such as changing the database and even replacing the framework.

Web, interface - the most external layer consists of frameworks and a database. For example, this level contains javascript code, spring, postgresql.

Figure 2. The dependency rule

A web application has been created that allows users to view advertisements for rental and sale of housing, with the analysis of optimal prices for the current period. The web application is based on the created architecture (Figure 3).

Figure 3. Web application interface

3. Conclusion

The creation and development of a model of demand for housing - a web application. The web application allows users to view advertisements for rental and sale of housing, with the analysis of optimal prices for the current period. And also it is possible to register users, log in to the system, create, edit ads, download images for ads with automatic change of permissions, search by parameters, create prices.

The studied and correctly compiled architecture made it possible to correctly create a web application that will function online. Drawing up the correct architecture simplifies maintenance, which reduces the cost of the project, and is also a more flexible system for further changes, such as a framework or database.

References:

1. Modeling methods and IS development models. http://inftis.narod.ru/pis/pis-p3-1.htm
2. Information System Architecture https://studme.org/282475/informatika/arhitektura_informatsionnyh_sistem#987
3. What is a database and database management system. http://ank.kz/post/chto-takoe-baza-dannyx-i-sistema-upravleniya-bazami-dannyx
4. Clean architecture. The art of software development. Robert Martin. - 2018 pp. 204-209.