I am very new to database design. I have a task to create an inventory program with  asp.net core and entity framework core.  The inventory program will be used to manage various kind of products. Products have some common fields (aka columns) such as:   ProductId Contidion (new, 2nd hand) Price  etc   But each product also has some specific fields. For example, a mother board has   MemorySlots (either 2, 4, etc) MemoryType (DDR2, DDR3, etc) CpuType (Amd, Intel) etc   Another product, for example, is a book. It has:   ISBN Authors  Title etc   Question  How can I manage the product-specific fields in a database?
What would be the optimum design/structure for product data database, where each product have many variations and many attributes? Attribute sets vary between products, and some attributes have values common for all variations of a given product. A typical example of product variations &amp; attributes table is in the image below:    (The 'ATTRIBUTE X' is here to give you and idea of a different attribute type than for 'Product 1').   Would it be practical to try to 'group' some of the attributes (to save time and minimise errors when creating new product entries)? If so, how complicated would it need to be?  If it's relevant - I'm thinking of using mySQL engine, but I'd be happy to see any applicable example from other engines.  EDIT : More information: at the moment we have over 400 variations in a spreadsheet, each one about 15-20 attributes, so that would give about 6000-8000 'data points'. It would be great to be able to list all possible values for a given attribute (to create a dropdown menu when adding new entries), and also to have a choice of possible attributes for a given product. It would be great to be able to specify which attributes are applicable for product variations of each product.
How to customize title page in beamer so that it looks like How can I modify title page so that it looks like it is in  video. Please seek to 16 seconds and watch title page. I do not have permission to post images. I liked this theme and I want to make a beamer theme that looks similar. I tried with beamercolorbox but I failed to position the box to the bottom.      Edit: Here is my minimum working example  \documentclass[xcolor=dvipsnames]{beamer} \defbeamertemplate*{title page}{customized}[1][] { \usebeamerfont{subtitle} \usebeamercolor[fg]{subtitle}  {\flushright \setbeamercolor{author}{bg=white,fg=Red} \usebeamerfont{author} \insertauthor\par \usebeamerfont{institute}\insertinstitute\par }  \vspace{0.2in}  \setbeamercolor{postit}{fg=white,bg=YellowOrange}  \begin{beamercolorbox}[sep=1em,wd=1.062\textwidth,ht=3cm,dp=3cm,right]{postit} \usebeamerfont{title} {\huge \inserttitle}\par \usebeamerfont{subtitle} {\insertsubtitle} \end{beamercolorbox} } \usecolortheme[named=YellowOrange]{structure} \useoutertheme{infolines} \setbeamertemplate{navigation symbols}{}  \institute{Harvard College Professor and\\ Johnstone Family Professor in Psychology, Harvard University}  \title{SAY WHAT?} \subtitle{Linguistics as a Window to\\ Understanding the Brain} \author{Steven Pinker}  \begin{document} { \setbeamertemplate{footline}{} \begin{frame} \titlepage \end{frame} } \end{document} I've upgraded from 4.4.0 to 4.4.8 and then 4.5.2 on Ubuntu 16.04 LTS 64-bit, and it's still happening.   At 4.5.2 it's even more frequent, and mainly in Chrome (haven't tried firefox or opera just yet). Every time I open a new web page. Any way to fix that, or is it a bug?  00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) 04:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Venus XTX [Radeon HD 8890M / R9 M275X/M375X] (rev 81)   Cheers. Trying to find a TV show about an event that leaves everyone dead apart from people who died at the moment of the event? This was a TV show aired in the UK probably sometime between 1990 and 1993, if memory serves it was only a one-off. The plot starts with the protagonist waking up in bed and being disappointed. He eventually goes outside and everyone is dead, whatever they were doing at the time they died doing it (driving, working, etc.) The protagonist is in a state of panic running around town (I seem to remember it being set in the UK) and he discovers that he's is 'alive' because he'd attempted suicide and died at the exact moment this mysterious event happened. I think he encounters others that 'died' at the time of the event and that's when he realises. I think the protagonist was a bald, white man, probably mid-thirties. Sorry for any vagaries, I was VERY young when it was on. Until recently I assumed it was The Quiet Earth but I've checked and it definitely isn't. It was in colour and was contemporary at the time so it would have been made around 1990. Why can't enum's constructor access static fields and methods? This is perfectly valid with a class, but is not allowed with an enum.  What I'm trying to do is store my enum instances in a static Map. Consider this example code which allows lookup by abbreivation:  public enum Day {     Sunday("Sun"), Monday("Mon"), Tuesday("Tue"), Wednesday("Wed"), Thursday("Thu"), Friday("Fri"), Saturday("Sat");      private final String abbreviation;      private static final Map&lt;String, Day&gt; ABBREV_MAP = new HashMap&lt;String, Day&gt;();      private Day(String abbreviation) {         this.abbreviation = abbreviation;         ABBREV_MAP.put(abbreviation, this);  // Not valid     }      public String getAbbreviation() {         return abbreviation;     }      public static Day getByAbbreviation(String abbreviation) {         return ABBREV_MAP.get(abbreviation);     } }   This will not work as enum doesn't allow static references in its constructor. It however works just find if implemented as a class:  public static final Day SUNDAY = new Day("Sunday", "Sun"); private Day(String name, String abbreviation) {     this.name = name;     this.abbreviation = abbreviation;     ABBREV_MAP.put(abbreviation, this);  // Valid } Does a Warlock receive the benefit of their familiar's Magic Resistance trait? The Warlock has access to special forms for their find familiar spell through the Pact of the Chain feature. I'm wondering if these special forms, the Quasit, Imp, and Pseudodragon in particular, allow the player character to share the familiar's Magic Resistance feature. In the Monster Manual each of these creatures has a sidebar that states that the familiar shares its Magic Resistance feature with the companion they are bonded to, but the PHB doesn't mention this in any of the creatures' stat blocks.   For example, in the Variant: Pseudodragon Familiar sidebar on page 254 of the MM it says:     "While the pseudodragon is within 10 feet of its companion,        the companion shares the pseudodragon's Magic Resistance trait."   This feature seems clear in the MM but I'm led to believe that it wasn't intended for Player Characters since mention of it is absent from the stat blocks in Appendix D of the PHB (pages 307-309).  Would a 3rd level warlock who chose one of these familiar forms through the Pact of the Chain feature benefit from advantage from saving throws from spells and other magical effects due to these special forms, or was this feature only meant for powerful NPCs and enemy spellcasters who had made this link with these familiars themselves? How can I highlight text before a character with listing? All is in the title. I would like to add a color to the text before a character with listing package.  For example, I would like to add a color to text between the beginning of a line and : or =, in a makefile.  I tried to use moredelimiters but I did not succeed.    \documentclass{article}  \usepackage{listings} \usepackage{xcolor} \definecolor{keycolor}{RGB}{172, 42, 42} \definecolor{mbleu}{RGB}{64,96,127} \definecolor{vimvert}{RGB}{46, 139, 87}  \lstdefinestyle{global}{   basicstyle=\ttfamily\scriptsize\color{black!90},%   stringstyle=\itshape\color{magenta},%   showstringspaces=false,%   keywordstyle={\bfseries\color{keycolor}},%   commentstyle=\color{blue}\slshape,%   framexleftmargin=1mm,%   backgroundcolor=\color{black!2},% }  \lstdefinestyle{makefile}{   style=global,%   morecomment=[l][commentstyle]{\#},%   emphstyle={\color{vimvert}},%   moredelim=[s][emphstyle]{\$(}{)}% }  \begin{document}  \begin{lstlisting}[style=makefile] .SUFFIXES: .inc .f .f90 .F  # all CPP processed fortran files have the extension .f90 SUFFIX=.f90  #----------------------------------------------------------------------- # this release should be fpp clean # we now recommend fpp as preprocessor # if this fails go back to cpp CPP_=fpp -f_com=no -free -w0 $*.F $*$(SUFFIX)  vasp: $(SOURCE) $(FFT3D) $(INC) main.o      rm -f vasp     $(FCL) -o vasp main.o  $(SOURCE)   $(FFT3D) $(LIB) $(LINK) makeparam: $(SOURCE) $(FFT3D) makeparam.o main.F $(INC)     $(FCL) -o makeparam  $(LINK) makeparam.o $(SOURCE) $(FFT3D) $(LIB) zgemmtest: zgemmtest.o base.o random.o $(INC)     $(FCL) -o zgemmtest $(LINK) zgemmtest.o random.o base.o $(LIB) dgemmtest: dgemmtest.o base.o random.o $(INC)     $(FCL) -o dgemmtest $(LINK) dgemmtest.o random.o base.o $(LIB)  ffttest: base.o smart_allocate.o mpi.o mgrid.o random.o ffttest.o $(FFT3D) $(INC)     $(FCL) -o ffttest $(LINK) ffttest.o mpi.o mgrid.o random.o smart_allocate.o base.o $(FFT3D) $(LIB) kpoints: $(SOURCE) $(FFT3D) makekpoints.o main.F $(INC)     $(FCL) -o kpoints $(LINK) makekpoints.o $(SOURCE) $(FFT3D) $(LIB)  clean:       -rm -f *.g *.f *.o *.L *.mod ; touch *.F \end{lstlisting}  \end{document} Understanding the differential $dx$ when doing $u$-substitution Finding a formula to sum natural numbers up to $n$ Possible Duplicate:          I got this question in homework:  Find an expression for the sum ‫‪     $\sum k = 1 +\cdots + n‬‬$.    and prove it using an induction.   I'm not even near finding the expression. What I did notice is that if $n$ is (for example) 5 then the sum would be   $5^2 - 4^2 + 3^2 - 2^2 + 1^2$  So the first number is always positive and from there on the sign changes.  Any tips on how do I contintue from this point on, assuming I'm in the right direction?  Thanks! What is the difference between French and British cuts of beef? What is the difference between French and British cuts of beef?   I am told they just butcher the animals dfferently. Certainly the cuts don't seem the same. For example is faux fillet really exactly the same as British sirloin and is entrecôte really the same as rib steak?  Here is a picture of British beef cuts. bash function cannot change the value of a local variable when called by $() The following code works differently depending on which way Parse_Short_Switches() is called.  After calling the function 'Parse_Short_Switches' by using result=$(Parse_Short_Switches), the value of $error_flag is NOT set to -1 as I would expect.  After calling the function 'Parse_Short_Switches' by simply using Parse_Short_Switches, the the value of $error_flag is set to -1 as I would expect.  Any help would be greatly appreciated.  Thanks  #!/bin/bash  function Parse_Short_Switches() { echo "error_flag inside of the function= $error_flag" 1&gt;&amp;2 error_flag="-1" echo "blah blah ..." }  # --- MAIN --- error_flag="999" echo "error_flag= $error_flag" #result=$(Parse_Short_Switches) Parse_Short_Switches echo "error_flag= $error_flag" how to remove object from NSDictionary Form of the Classical EM Lagrangian So I know that for an electromagnetic field in a vacuum the Lagrangian is $$\mathcal L=-\frac 1 4 F^{\mu\nu} F_{\mu\nu},$$ the standard model tells me this. What I want to know is if there is an elementary argument (based on symmetry perhaps) as to why it has this form. I have done some searching/reading on this, but have only ever found authors jumping straight to the expression and sometimes saying something to the effect that it is the "simplest possible". the (surely simplistic) model of a bipolar junction transistor one is taught in foundational physics course appears to be symmetric. - So, what is the difference between the collector and the emitter of a real BJT? If the transistor were symmetric one would not make this distinction...  Also:   Do BJTs have a 0.6V voltage drop like diodes? Are BJTs conductive in both directions, i.e. E-C and C-E?   Many thanks. Though tangentially related to another post on MathOverflow (), the questions below are mainly out of curiosity. They may be very-well known ones with very well-known answers, but...    Suppose $\Sigma$ is a sigma-algebra over a set, $X$. For any given topology, $\tau$, on $X$ denote by $\mathfrak{B}_X(\tau)$ the Borel algebra over $X$ generated by $\tau$.     Question 1. Does there exist a topology, $\tau$, on $X$ such that $\Sigma = \mathfrak{B}_X(\tau)$?   If the answer to the previous question is affirmative, it makes sense to ask for the following too:     Question 2. Denote by ${\frak{T}}_X(\Sigma)$ the family of all topologies $\tau$ on $X$ such that $\Sigma = \mathfrak{B}_X(\tau)$ and let $\tau_X(\Sigma) := \bigcap_{\tau \in {\frak{T}}_X(\Sigma)} \tau$. Is $\Sigma = \mathfrak{B}_X({\frak{T}}_X(\Sigma))$?   Updates. Q2 was answered in the negative by Mike (). This is the gift that my dad sent (to) me This is the gift that my dad sent me on my birthday.   Vs   This is the gift that my dad sent to me on my birthday.  Is to required?   Also   Presenting you guys, the trailer of the film.   Vs   Presenting to you guys, the trailer of the film.    Is to required? My windows directory is huge I have always had problems with my windows directory's growing to a huge size.  It started with windows 95 then 98 then 2000 and xp.  Windows 7 however is absolutely huge.  The windows folder itself with out program files is 21.4 gigs...add the program files and other windows files and it is a whopping 32 gigs.  My question is why is it so large and what can I do about it.  At the rate this is going I will be out of space in now time. Story identification: Old man has hacker neighbor who mysteriously dies Does anyone know this story? It was a novelette published with another one (I don't remember what it was) in . The premise was that the narrator is an old man whose neighbor, a hacker, dies under mysterious circumstances. A younger woman who is an expert in computer security is hired by the police to investigate what happened, and she has a fling with the narrator. After a while she dies as well, and the narrator realizes that it is an evil force that comes through electric lines is responsible for the killings. The title has interesting formatting in that it ends with a square (much like a command prompt cursor: [_] ) Why couldn't Bond have backup at the battle of Skyfall? I think I am missing a key plot point here.   Bond had to fake-kidnap M and bring her to Skyfall in order to lure Silva there for one last stand. Why did this have to be a secret from his colleagues at MI6? Why couldn't there have been other agents there to help defend the house and take down Silva?  Also, why did he have to have Q lay a fake trail to get Silva to follow him to Skyfall when he was actually going there, and he wanted Silva to follow him? Call a javascript function after 5 sec of last key press I have Ubuntu on my MacBook 2007 with a Spanish keyboard, on MacOS the @-sign was typed using Alt (Option) + 2, but on Ubuntu I have no idea. I have to copy and paste it every time. How do I type an at sign?