12 - Database Application Development
Table of Contents
- Welcome
- Application Development and Design
- Roll of Databases in Software
- N-Tier Development
- Design Methodologies
- Summary
Welcome to Week 12
For this week, we turn the page away from direct database work and look into the world of database application development and how the database fits into the world of software and software development. We will investigate the software development life cycle (SDLC) and then more specifically the database development life cycle (DBDLC) and their various steps.
This week the students will form groups and start to write a simple C++ program to complete a series of simple CRUD statements. The first and hardest part of this is getting the programming environment setup and establishing a connection.
Application Development and Design
The process of developing
software applications, whether they are web based, windows software, mobile applications and other, are
typically
developed in multiple tiers.
These Tiers typically include:
- Presentation / User Interface / View Layer
- Business Logic / Application Logic / Controller Layer
- Resource Management / Data Access / Model Layer
Each layer is called different things in different perspectives or in different software frameworks. They are essentially synonymous.
Model Layer
The model layer is often design to include software that represents the structure of the database and the DML statements and routines needed to manipulate the data, both reading and writing. This can be accomplished through creating a series of classes that represent the database entities (example: tables) with properties, constructors, and methods that are representative of the database CRUD statements.
Business Logic Layer
The business logic layer is the middle layer that takes input from the user interface and translates it according to business rules and application rules to forward it to the database layer for storage or retrieval. Once the data layer completes it's tasks, the data is sent back to the middle layer, processed, calculations are performed and the results are sent to the user interface appropriately.
The business logic layer is kept separate from the data access and user interface layer such that changes can be made to the business rules with little or no impact on the other layers, due to the separation of concerns in the software development process.
View or User Layer
The User-Interface layer often is a web site, mobile application or a windows application. Access between the user interface according and the business layer can be controlled through user access and role management and if often accessed through an API (Application Programming Interface).
Roll of Databases in Modern Software Development
Almost every modern software application has a database involved in the background. The purpose of the database could be:
- data storage
- data retrieval
- logging and tracking
- inventory management
- user and role management
- and many others....
Therefore, it is important that all software developers have a basic database design and implementation knowledge. In larger companies, software developers rarely touch the database, but even in this case, they still need the knowledge to work as part of the team and to assist with the development of the data model layers of the software.
In smaller development companies, where employees are often involved in many areas of the Software Development Life Cycle (SDLC). including database development, software development and the entire design process. The second half of this course concentrates of the database design aspects of this process and how building a strong database foundation is key to developing strong software.
N-Tier Development and MVC
The reason why a significant amount of software development is completed using the n-tier architecture is such that various aspects of the application can be kept independent for object oriented purposes. Keeping the layer independent allows them to be reusable, and multi-purposed.
The model layer can be shared amongst many different user interfaces and can be reused for many different versions of the application. For example, access to the model layer can be through an API ro directly in the case of administration access systems.
In some cases, software is divided into addition tiers to further separate concerns. One example of this: is to create a security layer that controls and centralizes user access, administration, role management, and permissions to perform specific actions within the business and data tiers.
Design Methods
When designing software, software companies take different approaches to each application developed and the decision is based on the application being developed, the client involved and the project scope and timeline.
Some of the approaches to database driven applications include:
- Bottom-up or database-first approach
- Top-Down or UI-first approach
- Inside-Out or Code-First approach
- Outside-In or Client Centric approach
Bottom-Up or Database-First Approach
This approach involves developing the database first in the application development process. This means that
a
significant amount of research goes
into the data requirements of the application through the requirements gathering process. Through database
modelling
processes and database normalization,
designers can come up with near complete database designs.
Pros
- developing the database first can ofter result in the ability to automate the code writing process through code generation.
- The coding of the data access or model layers can almost be completely automated
- Also, this approach typically results is fewer iterations and changes to the base foundation layers of the software which often results in smaller development timelines.
Cons
- This approach is sometimes difficult for clients to work with the software team as this approach often results in a long period of time near the start of the project where the client is not involved and would not see any progress that interests them, like screens or anything visible.
- This often results in the client wondering if the software company is performing its tasks, and a relationship breakdown between client and vendor.
- This approach also can result in limitations in the design of the design of the user interface due to code already being written. The iteration approach to the user-interface will be greatly limited.
Top-Down or UI-First Approach
This approach entails the design of the user interface first. The functionality of the system is defined
from the client's perspective. Many clients are most interested in how the
software works, how it looks and its' ease of use. Therefore,
this part of the application can be perfected with the client first.
Pros
- ensures early engagement with the client and this often results in more information and communication about software requirements and the ease of use.
- often results in a better user-interface design overall.
- focuses on final goals
- Addresses: functional issues such that the operations are supported and non-functional issues such as performance and availability
Cons
- this approach can lead to increased development time due to ensuring the coding can work for the given interface design. Also, although there is heavy engagement with the client early in the project,
- once the majority of the user-interface is complete, the client often believes the project is near completion, and gets impatient as the remainder of the application is developed without much interaction with the them.
- the system has to be developed entirely from scratch with little code generation or rapid application development techniques available
Inside-Out or Code-First Approach
This approach is similar to the bottom-up approach but focuses on the database access or model layer first built based upon the data requirements gathering process. This object orientated approach allows developer to create the required classes, properties and methods first and then generate the database from the code.
PROS: This approach works well for a team with strong developers, and can give the developers a deep understanding of all the code that will be accessed through the entire development process.
CONS: This approach often results in an incomplete database design and many criteria and database features missing, such is indexes, referential integrity and the use of stored procedures and user-defined functions.
Outside-In or Client Centric Approach
This approach uses the requirements gathering results and simultaneously designs both the database and user interface layers. Then as both ends are developed, they will work inwards towards the business logic layer.
PROS: This balances the client interactive parts of the development with those parts where very little client interaction is involved. This means the client sees continuous and consistent progress through the project and keeps lines of communication open.
CONS: This approach can often result in reiterating the design of both the user interface and data access layers because of considerations determined through the middle or business logic tiers.