Table «Student_Schedule» - Student Schedule of classes

Relationships

Columns	Association	Notes
	0..* Student_Schedule.student_id 1 Student.PK_Student
	0..* Student_Schedule.class_id 1 Class.PK_Class
	0..* Student_Schedule.term_id 1 Term.PK_Term

Table «Subject» - Some area of study in education

Relationships

Columns	Association	Notes
	0..* Subject.course_id 1 Course.PK_Course
	0..* Catalog.subject_id 1 Subject.PK_Subject

Table «Term» - Special Period of time, which has name, start date and end date

Relationships

Columns	Association	Notes
	0..* Class.term_id 1 Term.PK_Term
	0..* Catalog.term_id 1 Term.PK_Term
	0..* Student_Schedule.term_id 1 Term.PK_Term

3.4Activiti Database tables

The database names of Activiti all start with ACT_ (Figure 3.2). The second part is a two-character identification of use case of the table. This use case will also roughly match the service API.

ACT_RE_*: 'RE' stands for repository. Tables with this prefix will contain 'static'' information such as process definitions and, process resources (images, rules, etc.).

ACT_RU_*: 'RE' stands for runtime. These are the runtime tables, that contain the runtime data of process instances, user tasks,variables, jobs, etc. Activiti only stores the runtime data during process instance execution, and removes the records when a process instance ends. This keeps the runtime tables small and fast.

ACT_ID_*: 'ID' stands for identity. These tables contain identity information, suchas users, groups, etc.

ACT_HI_*: 'HI' stands for history. These are the tables that contain historic data, such as past process instances, variables, tasks, etc.

ACT_GE_*: general data, which is used in various use cases.

Figure 3.2 – Activiti database tables

Benefits

There are several benefits of this design:

• Normalized (each table has primary key)

• The weight of row in tables are low

• Tables have foreign keys

4Network and Servers

4.1Design

At Figure 4.1 we have a network grid diagram of the servers.

Let’s discover parts of network grid:

• Proxy Server -  is a server that acts as an intermediary for requests from clients seeking resources from other servers.

The purposes of using proxy server are:

• To keep machines behind it anonymous (mainly for security).

• To speed up access to resources (using caching). Web proxies are commonly used to cache web pages from a web server.

• To apply access policy to network services or content, e.g. to block undesired sites.

• To log / audit usage, i.e. to provide company employee Internet usage reporting.

• To bypass security/ parental controls.

• To scan transmitted content for malware before delivery.

• To scan outbound content, e.g., for data leak protection.

• To circumvent regional restrictions.

• Types of proxy servers:

• Forward proxy – is a proxy where the client server names the target server to connect to (Figure 4.2).

• Open proxy – is a forward proxy server that is accessible by any Internet user (Figure 4.3).

• Reverse proxies – is a proxy server that appears to clients to be an ordinary server (Figure 4.4).

We are using reverse proxy for our case of network design.

Figure 4.2 – Forward proxy

Figure 4.3 – Open proxy

Figure 4.4 – reverse proxy

• Load Balancer(NGINX) – is distributing service requests across a group of servers. The following diagram shows load balancing within a server. Addresses several requirements:

  • Increased scalability

  • High performance

  • High availability and disaster recovery

• Database Server – an independently functioning computer in a local-area network that holds and manages the database. 

• JBOSS AS – is a free software/open-source Java EE-based application server. There two nodes of JBOSS AS:

  • Node-1

  • Node-2

These Nodes operates between each other by round robin load balancing algorithm with session replication. Round robin – a simple algorithm that distributes each new connection/session to the next available server.

Figure 4.1 – Network grid diagram