Content Is Not Allowed In Prolog : Fix This Error

Content Is Not Allowed In PrologWhen learning to write code, it is so important to be aware of the kinds of errors that your coding could throw up. Rookie programmers often get hit with errors based on their bad coding practices and languages like Prolog do not allow certain types of content in certain areas of the program. All of this can be learned and is part of the learning curve of any junior programmer. We always find that minimizing errors is easily done if the beginner programmer tries their hand at some type of coding education. We like this course on Programming for Non-Programmers : Fundamentals of Programming as a nice introduction to the subject, as well as how to Learn To Program With Java as a great introductory course of programming in Java. Java is a great programming language as it can be called from many other programming languages and is supported on a wide range of systems.

Prolog is a simple, logic based programming language used a lot with computational linguistics and in artificial intelligence and creation. Prolog, as the name suggests, is based in the use of first-order logic or formal logic and uses a declarative computation system, which is different to most other languages. Running code based in Prolog is initiated by running queries over these declared variables. Prolog can call other languages and these errors that you are getting is due to this functionality. The Content Not Allowed error is actually an XML error, not a Prolog error and we will deal with this accordingly later on in the article.

As a programming language, Prolog is aimed for use with natural language and people often use it for things like gaming AI, automated question/answer systems and near-human control over any given system. Prolog is a great choice if the code you wish to create needs a GUI, and works well with networked application, given the correct commands.

A common error when new programmers are working with the programming language Prolog is “Content Not Allowed.”

This error is difficult to understand at first and we will be dispelling the mystery in this article.

Often, this bug is very difficult to find as you review your code. You and your other programming peers may not notice the error in a standard text editor as it is often caused by bad encoding of the text in the first place.

By going deeper and looking at the code to the byte level, the Content is not allowed error can be found and recreated by looking for errors coming from the Java XML parsers in Prolog. Most of the time, data is encountered before the declaration of the XML tags, which causes the error. As a rookie programmer, this is a difficult thing to spot and you may rewrite your entire program before figuring out what the problem is. Luckily, we are here to help you see the error. When you look through your code using something more appropriate and lower level, like a hexadecimal number editor, you will be able to see the problems as they occur.

You will find that when you are faced with the XML parsing error, your code is claiming to be written in a different encoding system from what the program expects. In most cases,  you will figure out that your code, which might be written in UTF-16 may be trying to run in an instance of UTF-8.

Programming is a difficult field to enter, yet highly rewarding and is a great way to show yourself how to think better. Even if you don’t wish to write code for a living, it’s a great idea to learn how to code as it will teach you how to use logic in your day to day lives and this can be very helpful, whether you are a programmer or not. Logic is a thing that is hard to understand yet infinitely rewarding once you do. This course on The Human Brain : Logic and Whole Mind Thinking, is a highly effective, quick course showing you how you can use your brain to help you in programming and any other field.

The Error in Prolog is quite easy to fix once you understand the problem. Other content not allowed errors can be caused by the byte order mark (BOM) before declaring the fact you are using XML inside Prolog and not declaring before you start using the actual XML  language to store content within the program. To fix this and get correctly functioning parsing of the XML content, you need to discard the BOM, so XMLPARSER can process the document. Often, this error can be fixed by taking your XML file into a text editor and deleting the strange sign before the first tag included in the XML file. This will only work if you have fixed any other Content Not Allowed errors as these will also throw up warning signals, which appear the same as the content not allowed error.

As you can see, the combination of Prolog and XML means that crossover languages can create strange, unaccountable errors. This is why most programmers choose a favored language and try to use this language instead of mixing and matching different languages to get their desired results. In Prolog, these Content Not Allowed errors are actually not caused by Prolog, as these errors are thrown up by the XML parser behaving “incorrectly.” Learning proper syntax and declaration strategy is integral to your success as a programmer and learning the Basics of XML will aid you in understanding this complex subject quickly and effectively.  XML is an extremely powerful way of keeping data and imminently flexible.

Hopefully, with the help of this article, you will realize not to call any XML variables before defining the XML tag in the Prolog language and you can say goodbye to the Prolog/XML error of Content Not Allowed error for good.